Part III

allows the axis of the first order to grow beneath the soil as a rhizome bearing cataphyllary leaves. In the axil of the third cata- phyllary leaf there is formed a vertical member of the second order which terminates in a flower (A. BRAUN). Case 3. Flowers are formed on members of the third order: " triaxial " flowers, three ranks. Example: Lathyrus. The mem- 184 COMPENDIUM OF GENERAL BOTANY. bers of the first order develop leafy shoots ; the members of the second order develop floral spindles (axes of inflorescence) ; the members of the third order finally develop flowers. The condition of affairs in the genus Pinus is especially note- worthy. Long shoots alternate with short shoots. The leaves (in clusters of two or more) occur on the short shoots ; the long shoots bear scaly leaves from the axils of which the short shoots are developed. PART IV. REPRODUCTION. INTRODUCTION. In the process of reproduction germs, or in other words foun- dations for new individuals, are formed. These germs usually separate from the mother-plant when mature ; sometimes they remain united to the mother-plant for a shorter or longer time, or even during the entire life-period. First case : The germs soon become separated ; in this case they have special structural adapta- tions for the purposes of protection, distribution, etc., and, above all, special physiological properties. The most important reproductive germs belonging here have specific names : seeds (phanerogams), spores (cryptogams). Second case : The germs remain in organic union with the mother-plant during the entire lifeperiod or only for a short time, (a) In mosses this union exists during the entire life-period of the plant, (b) In ferns the daughter-plant is set free by the gradual decay and disappearance of the mother-plant (prothallium). (e?) In propagation by means of bulbs, conns, runners, stolons, etc., the daughter- plant is made independent by the gradual disappearance of that part which unites it to the mother-plant. Daughter- and mother- plant may then exist side by side independent of each other. Reproduction, or the formation of new plant-individuals, is rarely limited to one method. In the same plant there are usually two or more methods of reproduction. The difference consists either (1) in that the germs are formed by different parts (organs) of the mother-plant ; or (2) that one germ is formed sexually, the other by one or several of the various asexual methods ; or (3) that 185 186 COMPENDIUM OF GENERAL BOTANY. the germs themselves and the plants proceeding therefrom are different. We can now recognize two categories of phenomena which may both be observed on the same plant at different periods. When different methods of reproduction are united in the same plant- individual, we are not concerned with alternation of generation. If different methods of reproduction do not occur in the same indi- vidual, but alternate with the successive generations of a plant, we speak, in general, of alternation of generation. By alternation of generation we therefore mean the unequal behavior of the successive generations of the same plant with regard to the mode of reproduction. Concerning the first-mentioned phenomenon we will not have much to say; considerable, however, in regard to alternation of generation. A B Let and represent different methods of reproduction (for example, sexual and asexual) ; they may be so distributed through the generations 1, 2, 3, 4, 5, 6, etc., that 1, 3, 5, etc., are the result A of the method ; 2, 4, 6, etc., of the method B. Of very fre- quent occurrence is that form of alternation of generation in which B method is common to a series of successive generations, while A method occurs in only one generation ; then another series of method B, etc. The following scheme will illustrate this : Series of Generations. MM BBBB REPRODUCTION. 187 propagated from stolons, runners, corms, etc. Should these latter means of propagation fail to appear, the plant could, nevertheless, continue its existence. At first glance the above general considerations and statements in regard to reproduction may not seem to have been very fortunately chosen. However, the student on entering more deeply into the phenomena coming under this category will soon recognize that the foregoing introductory statements, in which the author has followed KAGELI'S concept of the subject, are sufficient to place the essentials of the endless variety of phenomena under a few com- prehensive heads. Germ-formation is very frequently sexual, as has already been stated. The male and female organs, which are essential in this form of reproduction, permit of the recognition of three different forms, dependent upon the relative position of these organs. 1. Hermaphroditism : male and female organs are in imme- diate proximity, for example, in phanerogams in the same flower ; or on the same axis (among vascular cryptogams on the same pro- thallium). 2. MonoBcie : male and female organs are on the same plant,, but on separate axes ; that is, the flowers are unisexual. 3. Diweie : male and female organs are distributed upon dif- ferent individuals of the same species. A large number of flowers are hermaphroditic (perfect, bi- sexual), for example, our cereals, fruit-trees, legumes, the poppy, etc. ; the birch, oak, hazelnut, and most conifers are monoecious ; willows are dioecious. Monoacie and dioecie occurring together form didiny. Before entering upon the special discussion of the phenomena of reproduction it is important to introduce an observation on systematic botany. The essentials of our plant-system are taken from the domain of reproduction, and wre may add that, as far as mosses, vascular cryptogams, gymnosperms, and angiosperms are concerned, it is more than probable that no other factors will sup- plant in importance those of reproduction. Algae and fungi are separated from each other by the presence or absence of chloro- phyll, and both are separated from the leafy mosses by the absence of leaf and stem ; but within the algal and fungal groups them- 188 COMPENDIUM OF GENERAL BOTANY. selves the factors of reproduction are utilized in establishing classes, orders, and genera. From this we may draw the conclu- sion that in a book like the one before us, in which taxonomy is not more fully treated, the special chapters on reproduction must also give a general concept of the systematic arrangement of plants. I. EEPRODUCTION AMONG CKYPOTGAMS. We will speak first of the reproduction of cryptogams in gen- eral as compared with that of phanerogams. Generally the seeds of cryptogams are called spores ; they usually consist of one or of & few cells and are mostly microscopic in size. In contradistinc- tion thereto the seeds of phanerogams are larger and of a more complicated structure ; they consist of several parts. The perfect phanerogamic embryo within the seed-coverings has essentially the structure of a bud. Very frequently the spores of cryptogams are formed by asexual methods, and not as the result of fertilization. ' (SACHS proposed the term conidia ["gonidia"] for all thallophyte-spores produced asexually; EICHLER,' using the same term, applied it to the asexual motionless spores of fungi ; while WARMING wishes the term applied only to the asexual thallophyte-spores produced exogenously. It would no doubt be appropriate to follow the proposition of SACHS. 3 ) The seeds of phanerogams are, however the direct product of fertilization. There is also a series of cryptogamic spores which are the imme- diate product of two cells reacting upon each other. These spores are called oospores (egg-spores) when the two cells reacting upon each other are externally very different ; zygospores (zygotes) when the uniting cells seem to be entirely or almost entirely alike : the latter process is called conjugation. Most spores pass through a period of rest (resting- stage). With the maturation of the spores the plant for a time ceases 1 Compare GOBEL'S Grundzuge der Systematik. 2 Syllabus, 1886. 3 The term spores is, in general, also applicable to the reproductive organs of the so-called " " higher cryptogams mosses and vascular cryptogams ; they are also produced asexually. REPROD UCTION. 1 89 to exist as far as that particular generation is concerned, as. for example, during the winter, or during periods of dryness. These spores (" resting-spores ") usually develop at the next period of vegetation (spring, rainy season). On the other hand some spores develop soon after their maturation. They are usually endowed with a delicate membrane, as distinguished from the resting-spores, which have a more firm, usually colored, mem- brane. Such are the u " swarm-spores, so called because they can move about in the water until they prepare themselves for germination. As soon as they are ready to develop they come to rest or fasten themselves in some suitable place. (Algae and some fungi.) Sexual reproduction is not known to occur in all crypto- gams ; many investigators now agree with BREFELD that it does 1 not occur among fungi. Among the remaining cryptogamic groups algse (at least the great majority), mosses, and vascular cryptogams sexual reproduction undoubtedly occurs. The anther- ids are the male sexual organs (among cryptogams); they contain the fertilizing elements, the spermatozoids. The oogonidia, (egg- receptacle), or, when more complicated in structure, the archegoniay are the female sexual organs ; they contain the egg-cell. The spermatozoids are either very minute oval cells or, among the more highly differentiated cryptogams, spiral threads. These threads are usually supplied with two cilia (organs of motion) at the thinner anterior end ; the other end, which is usually thicker, contains plasm. The basal substance of spermatozoids (hence exclusive of cilia), according to more recent investigations (SCHMITZ, STRASBURGER, ZACHARIAS), consists of '( '' nuclein, that is, nuclear substance. The oogonium contains the egg-cell. In its simplest form the oogonium consists only of a covering for the egg-cell. The eggcell is frequently enclosed in a special organ known as the arche- gonium ; in its form it usually resembles an Indian club of variable length. In the archegonia of mosses and vascular cryptogams one may recognize a shorter or longer " neck " and an enlarged base (venter) containing the egg-cell. The figures will assist in illustrating and explaining what has just been stated. They refer to algse, mosses, and vascular cryptogams. Fig. 110 illustrates the 1 Perhaps also true of lichens ; as already stated, STAHL's observations have not been verified. TRANS. 190 COMPENDIUM OF GENERAL BOTANY. FIG. 111. Sexual organs of Vaucheria sessilis. Off, Oogonium ; a, antheridium. (After Sachs.) FIG. 110. Various stages in the of Spirogyra longata. (X 550.) (After Sachs.) conjugation Fig. 112. A, Rupturing antheridium of Funariahygrometrica (moss); B, magnified spermato- zoid in the mother-cell ; c, free spermatozoid of Potytrichum. (After Sachs.) REPRODUCTION. 191 processes of conjugation in Spirogyra longata ; the upper portion of the figure shows two segments, the cell-walls of which begin to form projections at a ; at b projections are in contact. Further A B progress is shown at at ; the final stages are shown. Such conjugating cells are called " gametes." " " Zoogametes is the B FIG. 114. Various stages of the antberidial development of Adiantum capillus (I, II, III), p, Prothalliutn ; a, antheridium ; s, spermatozoid with attached remnant of the mother-cell (6). (After Sachs.) FIG. 113. Funnria liygro- tnetrica. A, Archegonia (a) on the apex of the stem between the leaves (6) ; B, magnified archegonium (in glycerin) ; 6, ventral portion with oosphere ; h, neck of archegonium ; w, mouih of arche- FIG. 115. Longitudinal section of the archego- 1 ' P faf'ter" fertilization ) ^( Afte? nium of Adiantum capMu*, before fertilization. Sachs.) h, Neck ; s, ventral canal-cell ; e, oosphere, (After Sachs.) term applied to conjugating swarm-spores. Fertilization among Vaucheria differs very distinctly from that among Spirogyra ; in the former the oogonium og (Fig. Ill) is quite different from the E antheridium #; osp in is the oospore containing fat- or oil- globules. 192 COMPENDIUM OF GENERAL BOTANY. A. FORMS OF REPRODUCTION AMONG Although the phenomena under discussion differ very greatlyr we are enabled to see (among algae) a well-marked relationship ; there is, in general, an alternation of generation between sexual and asexual methods. Among Desmidiaoece (unicellular algse) asexual reproduction by division alternates with reproduction by the conjugation of mo- tionless gametes (see Fig. 19 in regard to reproduction by division). Peculiar and interesting conditions are met with among the 1 Diatomacew, a group of unicellular yellowish-green algse en- closed by a silicious mem- brane characterized by very beautiful and deli- cate striations and mark- A ings. highly delicate organization associated with great reduction in A FIG. 116. Diagramatic tation of two diatoms, view. B resenv teral FIG. 117. Top view of dia- tom. (Berthold and , Landois ) size characterizes these truly marvellous creat- ures. (E H R E N B E R (>, 1835. OTTO MULLER, Berlin, is at present well known as a specialist on diatoms.) Space will not permit a fuller discussion of the delicate structural markings ; we can only mention them in so far as they are concerned with the processesof reproduction. The two parts of the silicious shell of the diatom fit each other as do the body and cover of a pasteboard box. For a series of generations reproduction is the result of simple divi- sion, hence asexual ; then follows a special sexual generation (conju- gation), which is again followed by division, and so on (see Figs. 116 and LIT). The following statements are based upon direct observation. (1) Every division of a cell forming a diatom-individual (after cell-wall formation and separation of the two cells) gives rise to one (A) daughter-cell, equal in size to the mother-cell, and one (B) smaller daughter-cell. (2) There is no growth in length ; as a result the smaller individuals must continually increase in number. The 1 PFITZER made very important investigations of this group. REPRODUCTION. 193 species would therefore be gradually reduced to such small size as to render existence impossible. Extinction due to decrease in size is avoided by two methods. The first, after certain pauses, fully restores the original size of the individual. This is accomplished as follows : From time to time two small individuals unite with the escape and fusion of the cell- contents. This conjugation gives rise to cm exceptionally large individual, sometimes two. The second method is, so to speak, corrective, in that it tends to retard the decrease in size. OTTO MULLEB ' has discovered the fol- lowing law of development : The smaller of the two daughter-cells requires twice as long a period for the next division as the larger cell. The large spores formed by conjugation are called auxospores, and are sometimes formed from a single individual (without conju- gation). Protococcoideas,. Either vegetative reproduction by division, or sexual reproduction by the union of swarming gametes which differ in external appearance. Confervoidece. Asexual reproduction by means of swarmspores ; sexual reproduction by conjugation ( Ulothrix). Antherids and oogonia are formed in some cases (Oedogonium, Bidbochaetce). From PRINGSHEIM'S classical investigations of the alga Oedogonium I select the following : The oospore formed during the previous vegetative season produces four swarm-spores which develop into new filamentous algae. Swarm-spores are also formed from the vegetative algal threads. The oospore is the result of the fertilization of the egg- cell by means of the sperrnatozoids which enter through an opening in the covering of the oogonium. The sperrnatozoids are produced in two ways : either directly from the cells of an ordinary filament, or from a small few-celled male plant (Zwergmannchen). The latter is developed from an " androspore," a peculiar swarm-spore which, after liberation and swarming, comes to rest and, attaching itself in some suitable spot, devel- ops a few small cells. From these cells the spermatozoids, which finally escape and fertilize the egg-cell, are formed. Among Characece and Vaucheriacece there occurs a sexual propagation, besides sexual reproduction which is highly specialized in the former group. Among Characece propagation is accom- From the study of Melosira arenaria, Ber. cl. Deutsch. Bot. Ges. 5 I, 1883 194 COMPENDIUM OF GENERAL BOTANY. plished by means of the vegetative protonema (Zweigvorkeime) ; in the latter group occasionally by means of swarm-spores (A. BRAUN, PRINGSHEIM). Among Fucoidece sexual reproduction is known in only a few cases. Much is yet to be discovered, though in some respects our knowledge concerning the comparative significance of the phenomena of reproduction is quite exact. The difference in the phenomena of reproduction in Fucoidece and Floridece may be readily explained from a teleological standpoint. The spermato- zoids of Fucoideoe have cilia, therefore possess autonomous move- ment, while the fertilizing elements of Floridece (red marine algge) are without cilia, and hence motionless, and are called ' ' spermatia ' ' (o nepua, seed). In perfect harmony with such facts we find that the egg- cell of Fucoidece is first set free and is endowed with autonomous movement, and may be reached by the equally free swimming spermatozoids. Among Floridece fertilization is accom- plished by the female organ (" carpogone ") sending out a hair- like structure (" trichogyne ") from the fixed egg-cell to which the spermatia become attached. Floridece also reproduce asexually by means of '' '' tetraspores ; these are formed by each mother- cell dividing into four parts (BORNET, THURET, PRINGSHEIM, and others). B. FORMS OF REPRODUCTION AMONG FUNGI. The following is a brief summary of the chief forms of reproduction among the fungi. Asexual reproduction predominates. The asexual spores are produced either endogenously or exoge- nously. When exogenous, either basipetally or acropetally on the basidia or immediately on the mycelium. (The exogenous spores are sometimes called oonidia in distinction to the endogenously pro- duced endospores.) We will first mention the two groups Zygomycetes and Oomy- cetes in which sexual reproduction usually occurs. As the names would indicate, we have conjugation with the formation of zygo- spores in the former group, and oospore-formation in the latter group. In the genus Mucor endospore-formation also occurs, ("mould" on bread, fruit, old damp clothing, leather, etc., belongs to Mucor.) Finally, we will mention BREFELD'S chlamydospore-formation as an asexual mode of reproduction. By this is REPROD UCTION. 195 understood a '' secondary morphological '' change caused by some checking influence on the development of the sporangiophores, which then assume the function of spores. In a book of this kind it is well to adhere to facts obtained from actual observation, and not to enter into too many speculative considerations. Among the Oomycetes there occurs reproduction by means of conidia and swarm-spores, besides the formation of oospores, men- FIG. 118. Achlya lignicola. (After Sachs.) FIG. 119. Formation of swarm-spores in AcJdya. (After Sachs.) tioned above. As an example we may mention Achlya lignicola as one species of a group of fungi found upon dead flies and other insects, in water, etc. Fig. 118 (A-E) shows the oospore-formation. Fig. 119 shows the swarm-spore formation. The fungus Phytophthora infestans, which also belongs to this group, and which is so destructive to the potato-plant, has no sexual repro- 196 COMPENDIUM OF GENERAL BOTANY. ductive organs, at least none have so far been observed. It has verJy minute characteristic conidial spores. We shall now discuss the numerous fungi which have only asexual reproduction, namely, the Ascomycetes, J3asidiomycetes, Ure- dvnece, and Ustilaginece. The differences in reproduction as ex- pressed in the names of the first two groups are illustrated in Figs, ^^ FIG. 120--Asc 120 and 121. ores of Peziza ' Within the two large groups (After Berthoid and Landois.) Ascomycetes and Bdsiclwmycetes there is in each a sub-group without a sporocarp or covering for the spore-bearing tissue; the remaining sub-groups have sporocarps. In regard to the two genera Polyporus and Agaricus, it is to be observed that they represent the essential differences between the Agaricinei and Polyporei ; the lamellae (gills) in the one and the pores in the other are simply different arrangements of the Fig. 121. Fig. 122. FIG 121 and FIG. 122. Gills (lamellae) from the lower surface of a toad-stool. ^^^^^ a, Moderately enlarged; 6, basidium magnified.) 122, Lamt hyphal tissue especially adapted to give rise to spore-producing basidia. The following terms apply to the reproductive organs of many Basidiomycetes : peridium, gleba, and capillitium. The first'is the covering which encloses the entire spore-bearing tissue of the Gasteromycetes. Gleba is the inner hyphal tissue enclosed ' by the peridium. This hyphal tissue contains pores or chambers; the walls of these pores are called trama, and are lined with REPRODUCTION. 197 spores. The spores are set free by the rupturing of the peridium, while the cells of the trama enter into dissolution, except certain colls which form a loose network of hyphal filaments, the capil- litium. The Ustilaginece (blights) and Uredinece (rusts) form either single terminal spores or chains of spores. Among the UredinecB occurs a peculiar phenomenon called ' ' heteroecie ' ' (change of host) by its discoverer, DE BARY. Successive generations live upon different substrata, in this case upon different living plants (para- sitic). Heteroecie is known in about fifty species of rusts. The names '' '' blight and ' ' rust ' ' already indicate that we are con- We cerned with plant-diseases. will first discuss the hetercecious rust-fungi, then the blight-fungi. Puccinia graminis, the rust of our grasses, especially grains, is far more injurious than the blight-disease. Blight is limited to single plants of our cereals, while rust appears epidemically by its rapidly formed and germinating summer-spores. The methods of exterminating this plant-disease are as follows : 1. To destroy the 4 ' intermediate ' ' host, which serves as a substratum for one generation : in Puccinia straminis the jBorraginece, and in Puccinia graminis the shrub Berberis vulgaris (see Fig. 123). 2. To de- FIG. 123. A, Young aecidium ; /, mature aecidia (a) on a lenf-sectiou of Berberis vulgaris ; B, highly magnified telentospore of Puccinia graminis. (After Sachs.) stroy as many as possible of those plants which shelter the teleuto- spores during the winter months, that is, the remnants left in the 198 COMPENDIUM OF GENERAL BOTANY. grain-fields. 3. Grasses growing wild in the grain-fields (example : Triticum repens) often serve as hosts to the fungus. These must also be destroyed. The course of development in Puccinia graminis is as follows : (a) The fungus lives upon the leaves of Berberis vulgaris during the spring and produces seeidiospores (Fig. 123, 7&, A), which are carried to the wheat- or oat-plants by the wind ; (&) germina- tion and growth begin at once and end with the formation of uredospores, which may be carried to other plants and also develop. (The spermagonia and spermatia shown in Fig. 123, sp, are little understood. Formerly they were supposed to be male sexual 1 organs. ) The earlier che fungus attacks the plants the more in- jurious are the effects. Sometimes all the leaves are infected, even the glumes. Toward the close of the vegetative period (<?) teleuto- spores are formed, which remain at rest during the winter months and begin to germinate in the early spring. From them grows (d) &promycelium with sporidia. The sporidia develop upon suitable hosts (in this case upon the leaves of Berberis) and again form secidiospores, thus forming the beginning of a new cycle of development. Tilletia Caries causes the smut of wheat; various species of Ustilago cause the blight of different grasses, especially of oats, barley, and wheat. (To prevent the occurrence of both of these fungi it is necessary to soak the seed to be sown in a J per cent solution of sulphate of copper for about twelve or fourteen hours and then to sow the seed during dry weather.) In this disease spore-formation takes place in the ovarium with destruction of the ovulum, while the assimilating organs (leaves and stems) are not attacked, as in rust-diseases. The spores adhere to the outside