SUBSTANCE AND FORM OF ORGANS. g 



and their existence, to which I replied at the time ', is only possible if, as has happened 

 hitherto, the organic form is regarded as something existing per se; as if the organs of 

 the plant themselves by no means consisted of real matter, with its forces and reactions 

 to external influences, but, like platonic ideas, existed only in the abstract, but were 

 nevertheless able to operate upon the actual matter of plants. 



If now the outward form and internal structure, and the functional capacity of 

 an organ resulting therefrom, constitute the necessary expression of its material sub- 

 stance, then a very simple consideration leads us to the perception, that this material 

 substance of an organ is itself again the result of the physiological activity of preceding 

 organs of the same plant. The first organs of the seedling arise from materials 

 or chemical compounds, which the mother-plant has produced and apportioned 

 to them ; the later organs arising after germination, the shoot and its parts, roots and 

 so forth, however, are constructed from the materials which the organs of the seedling 

 have taken up from without, and then further altered according to the specific nature 

 of the plant ; each subsequent organ is the result of the constructive activity of 

 preceding organs. Thence it follows that the construction of organs, their deve- 

 lopmental history and growth, is also a subject-matter of vegetable physiology, 

 and that, as one may say, not only the most important but also the most 

 difficult part of it. Vegetable physiology has thus to do not merely with the 

 functions of organs already existing, but also with the origination of the organs 

 themselves, which is itself a function of preceding organs. In reproduction, we must 

 assume that certain particles of matter pass over into the reproductive cells, which 

 have been previously produced and their nature determined by the organs of the 

 mother-plant, and now possess the capability, whilst appropriating to themselves new 

 matter from without, of imprinting upon this the same series of material diflferences 

 as had already declared themselves in the mother-plant''. This repetition of the 

 formative processes which depend on chemical processes is, as a rule, a very exact 

 one in each organic form, so that the descendants resemble the progenitors in all 

 points. It is this process which is termed Heredity. It is at once perceived that 

 Heredity is simply a fact of experience, the cause of which we do not know, and 

 nothing more. It can therefore only lead to more complete confusion in science, if, 

 as often happens in these days. Heredity is treated in a very thoughtless manner as a 

 force of nature, by which it is imagined to be possible to explain all manner of things. 



But this constant repetition of the peculiarities of the ancestors in the de- 

 scendants is not without exception ; sometimes, as cultivated plants especially show in 

 a thousand ways, more or less extensive deviations from the peculiarities of the parents 

 appear in the descendants, which, under certain circumstances, may become more and 

 more intensified in the following generations, by further propagation. This fact is 

 expressed by the term ' formation of varieties.' Its cause is in general unknown ; in 

 any case, however, we are correct in assuming that the changes, perceptible externally 

 ■ in variation, consist in material alterations in the parents, during procreation or 



' Compare my treatise ' Staff und Form der Pfianzenorgane ' in the Arbeiten des botan. Instituts 

 in Wiiizburg, 1880, Bd. II, p 453. 



' I have explained in my two treatises on ' Staff und Form " in the Arbeiten des botan. Instituts 

 in Wiirzburg, Bd. II, that the 'gemmules' in Darwin's Pangenesis are not meant here, but matter in 

 the sense of chemistiy and physics. 



