Hereditary Variation and Selection

Furthermore, crossing would continually tend to re- move the incipient variation. 4. Nutritive influences do not produce hereditary changes. 5. According to Darwin's theory of selection, the more useful a property of an organism is the more constant it must show itself in the process of selection ; structures which do not prove advan- tageous must be variable. It has been observed, however, that in the plant kingdom the laws of cell-division and other morphological characters are the ones which prove to be exceedingly constant ; these certainly have nothing to do with selection. Here Nageli also includes phyllotaxy (to be discussed later). Space will not permit us to enter into a fuller discussion of Darwin's theory and Niigeli's objections thereto. Although Nageli calls his theory the " theory of direct cause," it does not assist in elucidating matters when he assumes that it is the unknown structure and mechanism of the idioplasm which causes the evolution of the organic world. With such total obscurity in regard to our knowledge of idioplasmic mechanism we certainly cannot rationally speak of a "direct cause." Therefore we cannot recognize a theory of direct cause for the existence of and descent of plants in the sense that this existence is a natural result, and not a special creation. The micellar constitution of idioplasm, which gives rise to the processes of life, must be designated as a special gift of the Creator. Nageli admits that the primordial plasm is converted into idioplasm by the given (inherent) molecular forces. As Nageli states that there are causes inherent " by nature" in the idioplasm, so we likewise, from the idealistic point of view, state that this or that happens according to nature. We, however, wish to imply that the natural laws as well as matter itself are derived from God, and therefore we speak of the existence of a special creation, We and not of a natural necessity, which controls all. will even go so far in the use of language, in so far as we are dealing only with the natural laws of creation, that we will not speak of u miracle," although we believe in the miraculous creation and preservation of We the universe by the Creator. leave the pale of science only when the sum-total of scientific investigations fails us. Although Nageli has clearly shown the fallacies of Darwin's theory, he has allowed himself to fall into gross errors in regard to his own theory (for example, in regard to the influence of external 250 COMPENDIUM OF GENERAL BOTANY. stimuli, the behavior of idioplasm). His logical mind, however, finally led him to that substance whose mechanism we cannot understand, but which science has long considered as the sustainer of the various life-phenomena, namely, plasm. In this substance we also believe the forces to be concentrated which enter into the phenomena of life and growth. With idioplasm, the structure and mechanism of which Nageli considers the "greatest mystery in the doctrine of descent," we also associate the miracle of creation ; we know that " living " plasm is necessary for the existence of a living cell, and hence for every living plant. "Mystery" and "miracle" are the two contrasting terms. Let our opponents not be misled : idealist and materialist both fail to comprehend the natural causes of certain things. The idealist knows from experience that the thorough investigation of any phenomenon in nature will sooner or later meet with conditions which must be looked upon as given. The materialist ignores this experience, does not explain the " mystery," but still maintains that the ultimate causes are capable of a natural explanation without miraculous intervention. Is it not well for the human mind, which is only a breath of the creative Spirit, to recognize one's Creator in nature ? Is it, then, intellectual weakness to acknowl- edge the Almighty ? Why did Nageli write, " To deny spontaneous generation is to declare the miracle"? Although we declare the miracle, we are stricter empiricists than our opponents; we also value scientific investigations which bring to light truths which the human intellect can arrive only at after much toil. APPENDIX. The Life-period of Plants. 1. The Schizomycetes live about 3-J hours on the average, after which the individual divides(NAGELi and SCHWENDENEE). 2. Moulds and microscopic algse live from several days to sev- eral months. 3. Many plants live one or two, more rarely several, " vegetative periods," which vegetative period may extend over a period of from J to f of a year. Winter in the temperate zones and the dry period in hot climates is the time of vegetative rest or seed -rest. Accordingly we speak of annual, biennial, or perennial plants (see p. 158). REPRODUCTION. 251 We also find that biennial plants of our climate become annual in warmer climates ; perennial plants of warmer climates sometimes be- come annual in our climate (Ricinus). 4. Tree-like plants sometimes reach an old age. Of our indige- nous trees the linden, oak, pine, and yew may become 1000 years old, the yew even 3000 years. Among conifers the ages of Taxodium distichum (Mexico) and Wellingtonia gigantea (California) have been estimated at 4000 years. Of monocotyledons, Dracaena Draco (Teneriffe) reaches the age of several thousand years. The climax of mass development and age is reached in Adansonia digitata (Africa), which is said to live 6000 years. At the moderate height of 9-12 m. this tree measures 30 m. in circumference, and has branches 15-18 m. long (SEUBEKT). We are in doubt as to the exact age of many subterranean rhizomes and perennial plants, since we have not actually observed how long a rhizome may live. PAET Y. THE GENERAL CHEMISTRY AND PHYSICS OF PLANT-LIFE. I CHEMICAL PHYSIOLOGY. In the treatment of tissue-physiology (II, B) we also took into -consideration some very important chemical processes, such as assimilation and the formation of albuminous compounds. It now remains for us to consider the more important features of the general chemistry of plants. (In the main we will follow PFEFFER and SACHS.) As a rule, the first step in making an analysis of a plant-substance is to place the substance to be examined in a desiccator. The deter- mination of the dry substance and water of different plants gives widely different results, depending upon the conditions of develop- ment. Ripe seeds contain comparatively little water, the dry sub- stance constitutes about of -f the entire weight, while in the germi- nating seed, after the reserve material has been absorbed, it is scarcely TV ; later the weight of the dry substance may again increase from J to -J. In submerged plants there is of course but a very small amount of dry substance, often less than -^. On burning the plant only a small percentage remains as ashes. This important statement implies that almost the entire mass of the dry substance must consist of combustible or volatile elements or compounds; the elements are C, H, N", O. S remains in chemi- cal union with the ash, forming basic oxides, similar to the readily oxidizable P. What are the substances appropriated by the plant, and how are 252 THE GENERAL CHEMISTRY AND PHYSIOS OF PLANT-LIFE. 253> they appropriated ? What substances are absolutely necessary, and why? C, H, O, N, also K, Ca, Mg, P, and S, are the elements of which the food-substances are composed. Na, Cl, and Si seem to belong to the group of useful rather than necessary elements. Among K fungi, rubidium and caesium may be substituted for ; Mg, Sr, or Ba for Ca. Fungi may subsist without Fe, since they contain no chlorophyll. lV[arine-plants contain iodine and bromine in addition to the elements mentioned above. N Among plants and are the only elements which occur in K O the free state as a gas, as a gas and in solution in water. The remaining elements occur almost exclusively as binary, ternary, or even higher compounds. Since plasm is chemically closely related to albuminous com- pounds, and since the cell-wall and starch consist of carbohydrates, it becomes evident that C, H, O, N, S are the necessary elements,, eventually also P. Oxygen alone enters into the plant-metabolism as an element. Iron enters the plant in the form of an oxide in solution. It occurs only in small quantities, though it is absolutely necessary in chloro- phyll-formation and therefore also in assimilation. Sulphur and sometimes phosphorus are necessary in the formation of albuminous- substances. Potassium and calcium are also necessary, though their true significance is not understood. (See below.) According to BOUSSINGAULT, the free nitrogen of the air cannot be utilized as food by the plant. It is usually introduced into the plant by way of the roots ; not in the free state, but in the form of compounds, such as nitrates, nitric acid, and ammonia in solution in water. In the years 1851-1854 Boussingault apparently demonstrated the fact that when all nitrogen-bearing compounds were ex- cluded from the soil and atmosphere, the elementary !N" did not in- crease the nitrogenous compounds of the plant; the plant would die after all the reserve nitrogen in the form of compounds had been util- ized. This belief prevailed until recent years, when YILLE, JOULIE, ATWATER, FRANK, HELLRIEGEL, and others carried on experiments which tend to prove that the free nitrogen of the air may be utilized by the plants. FRANK based his conclusions upon experiments with algae, fungi, and several phanerogams. He has demonstrated that not only are leguminous plants which bear root-tubercles containing 254 COMPENDIUM OF GENERAL BOTANY. fungi (rhizobia) capable of assimilating free nitrogen, but also non- leguminous plants, as opposed to the conclusions of HELLEIEGEL. We will now return to the important nitrogen-bearing com- pounds. According to BOUSSINGAULT, phanerogams appropriate nitric acid more readily than they do ammonia ; for some fungi ammonia is better suited than nitric acid (PASTEUR, A. MAYEE, NAGELI). Sulphur said, phosphorus enter the plant in the form of sulphates and 1 phosphates. H The two binary compounds CO 2 and O2 supply the plant with CO the elements C, O, and H. is 2 almost exclusively takon from H O the atmosphere, 2 almost exclusively from the soil. The process CO H O of assimilating and 2 2 necessitates the presence of chlorophyll CO and the aid of sunlight. For each volume of 2 assimilated there is liberated an equal volume of O. The most common product of assimilation among dicotyledons is starch (amylum), which occurs in H O the form of small grains. If we consider C 6 JO 5 as the formula for this compound, the reaction may be represented ae follows : + = H + 6C0 5H 2 2 C 6 10 6 120. In other instances (many monocotyledons) a form of sugar seems to take the place of the starch (see pp. 122 and 131). So far we have not been able to follow the process of assimilation in its various phases. In the circulation of food-substances within the plants, the processes of catabolism, such as converting starch and cellulose into sugar, decay, etc., are much better known than the processes of metabolism (assimilation and various processes of transformation. (See p. 258). At present we have not a clear understanding of the part that chlorophyll plays in the process of assimilation. In the discussion of the assimilating system we learned that the influence of light varied with the wave-lengths (color) ; this relation was made clear 1 According to SACHS, the following is a very satisfactory culture-fluid for plants: Water 1000.0 cu. c. Potassium nitrate , Chloride of sodium Sulphate of calcium Sulphate of magnesium Phosphate of lime (finely pulverized) Chloride of iron l.Ogram. .5 " " .5 .5 " " .5 a few drops. THE GENERAL CHEMISTRY AND PHYSICS OF PLANT-LIFE. 255 by ENGELMANN'S interesting bacterial experiments, which confirmed We the old theory of LOMMEL. shall now return to the nitrogenous foods. The following are natural sources of nitrogenous compounds. NO; 1. The electric spark passing through dry air produces this NO O immediately unites with the of the atmosphere and forms 3; the latter unites with water to form nitric acid : O N0 H2 NO, HO 2. In various processes of combustion ammonium nitrite and NO NH NO ummoniurn nitrate are formed (NH4 3 , 4 3 ). 3. Ever since animal creation the decay of animal substances has been the source of important nitrogenous compounds, especially NH 3 (ammonia). Connected with this process of ammonia-forma tion is 4. The production of saltpetre (potassium nitrate), as follows : NH O 3 takes up in the presence of an alkali ; that is, the oxidation NH NaNO of KNO, 3 forms a nitrate, as , 3 ; the latter occurs very plentifully in Chili. The formation of albuminous substances in the plant has already been discussed. Mineral Food-substances. The essential minerals are K, Ca, Mg, Fe (S and P were mentioned above). The agricultural impor- tance of phosphate of lime, of the sulphates, and of the lime-salts are well known. Cl, Na, and Si are useful, though not necessary. The true use of K. that is, of its compounds, is still unknown; it always seems to be concerned in the translocation of plastic materials. It is probable that Ca plays a part in the formation of Mg cell-walls. seems to be distributed much in the same manner as K. Of Fe we know definitely that it is necessary to the forma- tion of chlorophyll. (This seems to be the reason why fungi can do without it.) According to the recent investigations of F. W. SCHIMPEB, Ca serves as a vehicle for the mineral acids, especially phosphoric and sulphuric acid ; it furthermore prevents poisoning by preventing the accumulation of acid calcium 1 oxalate. Flora, 1890. 256 COMPENDIUM OF GENERAL BOTANY. With the following enumeration of chemical combinations and mixtures of combinations only a few explanatory statements are given; further detailed information in regard to them has already been given and may be referred to by the aid of the index. Carbohydrates, albuminous substances, tannin, oils, fats, wax, amides, resin, coloring-substances, ferments. Of the glucocides (whose formation and importance in the planteconomy is still unknown) we may mention amygdalin, salicin, digi- tatin ; of the bitter extracts, lupulin and aloin. According to PFEFFER, and more especially to BE TRIES, one physiological activity of vegetable acids, that is, their salts, is that they increase the hydrostatic pressure of the living cell by produc- ing endosmotic action. The nitrogenous organic com pounds of a basic character, namely, the alkaloids, must also be mentioned. They are very frequently found in the laticiferous ducts of various plants. In the milky juice of the poppy (opium-plant) are found thebaine, morphine, and other alkaloids; in the bark of the Cinchona, trees is found the alka- loid quinine' strychnine is found in the seeds of Strychnos; atropine, daturine, hyoscyamine in the Solonacece, etc. These compounds have a poisonous effect upon the animal organism, and may there- fore serve the plant as a protection against the attacks of animals. Resins occur not only in conifers, but also in various exotic plants. Incense is a resinous product of Boswellia Carterii ; myrrh, of Commiphora (Balsamodendron} Myrrha (WARMING). According to HOFPE-SEYLER, cholesterin, which is widely dis- tributed in seeds, is a secondary (catabolic) product of the albumi- noids. Leaving chlorophyll out of consideration, there are many other We coloring-substances occurring in the vegetable kingdom. will refer only to those usually associated with chlorophyll. Red, brown, brownish-yellow, and blue-green coloring-substances are met with among various algse. Here also belong the coloring-substances of flowers and fruits, of fungi, the coloring-substances in various barks. Examples: the kino-red of Pterocarpus Marsupium (FLUCKIGER) and the coloring-substances of other woods (ebony, etc.). In connection with the characteristic process of carbon-assimila- tion it must be impressed upon the beginner in the study of plant- CO physiology that there is a true respiration with liberation of and 2 CO assimilation of O, besides the usual appropriation of and libera- 2 THE GENERAL CHEMISTRY AND PHYSICS OF PLANT-LIFE. 257 tion of O. This true respiration is, in general, necessary for the life and growth of plants. Based upon the investigations of BOUSSIN- GAULT, GARREAU, SACHS, PASTEUR, NAGELI, and PFEFFEK, we may for- mulate our present knowledge in regard to this subject as follows. 1. If we consider the chemistry of fermentation in plants (the CO conversion of sugar into 2 and alcohol, and other similar processes) as " intramolecular respiration," 1 we may make the general state- ment that no plant can live without respiration. 2. Some of the energies necessary to cell-life -are due to respira- tion. 3. Oxygen is also necessary for the existence of some fungi if they are not supplied with substances capable of undergoing fer- mentation. Fermentation enables them to exist without the respi- O ration of without fermentation ; growth ceases unless oxygen is supplied. 4. Respiration continues as long as the normal conditions of life exist ; it is most active in the growing plants and growing parts of plants; for example, during germination and during the develop- ment of tubers and buds. Within certain limits respiration increases A with the rise of temperature. direct influence of light upon the respiration of chlorophyll-less parts of plants has not been observed. Chlorophyll-bearing parts of plants assimilate only in the presence of sunlight, but respire in the dark as well as in the sunlight. " Selection." We usually speak of plants as having the ability to " select n certain food-substances. The true explanation of the meaning of this term is as follows. It has been known for a long time that dif- ferent plants growing in the same environment take up the same food-substances in different proportions ; for example, Nympkcea alba and Arundo phragmites, both of which grow in water or in marshy soil, and which are therefore in contact with the same soluble food-substances, take up SiO in 2 widely different proportions. The former plant contains usually less than ^ per cent of silica, the latter usually more than 71 per cent (SCHULTZ-FLKETH). From un- 1 According to PFLUGER (1875), intramolecular respiration takes place in an atmosphere free from oxygen with liberation of CO 2 due to the breaking up of compounds within the cell ; "normal" respiration is accompanied by oxygen- assimilation. 258 COMPENDIUM OF GENERAL BOTANY. known causes inherent in the individual these two plants require different amounts of silica in the building up of the body-substance (deposition in the cell-walls, etc.). Due to causes inherent in the processes of osmosis the nutritive cells of Arundo allow more SiO, to enter, because it is continually removed and utilized elsewhere, while in Nymphaea SiO 2 is not removed from the cell. As we have already learned, the living primordial utricle possesses the property of being impermeable to certain substances in solution (as sugar, coloring-substances, etc.). This property is due to the inherent peculiarities of the plants themselves, and not to any " selec " tive power. THE CYCLIC COURSE OF FOOD-SUBSTANCES. The entire chemism of plants may be diagramatically repre- sented upon a circular line, dividing it into quadrants as follows : 1, assimilation ; 2, transformation ; 3, retrogressive changes ; 4, decomposition. 1 and 2 are metabolic processes, 3 and 4 catabolic (NAGELI). CO H NH HNO a, aO, and 3 (or 3) figure as raw material in the first process and again appear as the final products in process 4, in decay, fermentation, etc. Processes of transformation convert the carbo- hydrates and amides of process 1 into more complicated chemical compounds, as cellulose, albuminoids, fats, ethereal oils, etc. Retro- gression (3) works in the opposite direction ; cellulose is changed into sugar, fats into fatty acids and glycerine ; glucocides are also split up into sugar and some other compound. The products of de- H NH composition (4) are again the simpler compounds CO,, aO, . 3 II. THE PHYSIOLOGY OF GKOWTH. Scientific botany, like other special sciences, finds its greatest difficulty in solving those problems which lie nearest at hand. Why What is growth ? must cells grow ? These are questions which the physics and chemistry of plants have failed to answer sat- isfactorily. Growth, the specific manifestation of life, like all other vegetable life-phenomena, can be traced only to plasm, in which it is inherent. There is no mechanics of plasm which enables us to deduce from the structure and peculiarities of plasm what actually occurs in the growing cell. This statement is to be emphasized, be- THE GENERAL CHEMISTRY AND PHYSICS OF PLANT-LIFE. 259 cause efforts have not been wanting to explain the growth-phe- nomena in ' cell-life from a purely physical basis. (See below.) A cell must have a certain degree of turgor as a necessary con- dition of surface-growth ; hence turgor is a phenomenon always accompanying surface-growth. Frequently the ratio of growth proceeds parallel with the turgor-force (DE TRIES). Our knowledge of turgor is, however, far from sufficient to give us a clear conception of growth. There are certain substances known to physiological chemistry which form vesicular deposits, the so-called membranes of precipitation, as, for example, lime solution and tannin, sulphate of copper arid potassium ferro-cyanide. To these " " inorganic cells (vesicles) the " " turgor-growth theory is to a certain extent appli- cable : taking up of water by endosmosis causes the artificial mem- brane to expand and finally to rupture. At this rupture the solu- tions within and without at once form a new membrane of precipi- A tation ; this may be repeated again and again. cylindrical algal cell, however, differs very materially from such artificial vesicles, because it has a cellulose-membrane and plasmic utricle, and the cell-wall can grow only with the aid of the plasm. In its chemical nature the membrane is not merely a precipitate from the albumi- nous substances and water. Continuing the comparison, one would expect that the cylindrical cell would become nearly spherical in a short time because of the equal expansion in all directions. Actually it elongates in one direction, which indicates that a difference in the expansion of the cell-wall in different directions is one of the con- ditions of cell-growth. A. ZIMMERMANN* gives a brief summary of the efforts made by different authors to give a mechanical explanation of the form and We position of cell- walls. must estimate the work of BERTHOLD and ERRERA especially. I say " estimate," because it is very important that we should not draw other conclusions than such as really follow from the results of their investigations. According to Zim- mermann, the following may be looked upon as being established by the investigations of Berthold and Errera. It is an empirically derived rule rather than a generally estab- lished fact that the cell-wall during cell-division begins as a surface 1 BERTHOLD, Studien iiber Protoplasmamechanik, Leipzig, 1886. TRANS. * Beitrage zuv Morphologic und Physiologic der Pflanzenzelle, Tiibingen, 1891, Heft 2. 260 COMPENDIUM OF GENERAL BOTANY. of smallest area. Although the young cell-aggregates resemble the vesicles of soap-suds in their arrangement and in the position of the 1 walls, yet it must not be assumed that this offers a mechanical ex- planation of cell-wall formation. The attempt to explain the me- chanics of the exceptions to the rule seems especially futile. Further, every anatomist knows that in the development of plants and plant- organs we are not only concerned with cell-aggregates which are divided by surfaces of least area: the cell- walls are intimately cor- related to the form of the organs as well as to the ultimate function of the cells. All that we can comprehend of this correlation is that it serves a specific purpose. Berthold himself does not give an exact mechanical explanation of the arrangement of cell-walls. The growing cell-wall (for example, of