VARIATION. ADAPTATION. ORIGIN OF SPECIES 391 



But we can scarcely rest satisfied with.this hypothesis only ; we must also assume 

 a definite capacity in the plant of establishing certain adaptations by heredity, and 

 this capacity is certainly not universally possessed. To this view, however, 

 scarcely any exception can be taken, since it is a well-known fact that the 

 capacity for adaptation is especially pronounced in some circles of relationship 

 whilst it is absent from others. This is shown very strikingly by the way in 

 which some families among higher plants tend to a parasitic or carnivorous habit 

 while others exhibit no such leaning. Similarly, a tendency to inherit an adapta- 

 tion to an aquatic or to a xerophytic life may exist here and there, whilst other 

 plants, perhaps, have, on the contrary, lost that adaptive capacity. Two prin- 

 ciples, in a certain degree antagonistic, make themselves evident here, the one 

 aiming at making the plant as many-sided as possible and so permitting it to 

 find a footing in numerous different situations, the other making it one-sided 

 but also gifting it with the capacity of adapting itself to one extreme condition. 

 If all organisms made exactly the same demands on the environment their 

 continued existence would be a mere matter of days. The correctness of this 

 conclusion has already been emphasized elsewhere (Metabiosis, Lecture XIX). 

 Weighty objections to the inheritance of acquired characters have been 

 advanced in the animal world, especially by Weismann. He (1892) regards 

 adaptations as acquired characters, and tries to show that inheritance of these is 

 theoretically impossible and has never been established practically. This view 

 of acquired characters is, in the first instance, based on a study of the animal 

 world, where there is frequently a sharply marked demarcation between germ and 

 somatic cells from the very commencement of the divisions in the egg-cell. The 

 peculiarities which occur in the somatic regions induced by external influences 

 or functional stimuli are regarded as acquired, or originating during the life of 

 the individual, in contrast to those which are inherent, that is, whose initials 

 were already present in the ovum. We may distinguish four types of acquired 

 characters: (i) mutilations; (2) diseases; (3) adaptations to external conditions ; 

 (4) functional adaptations. Botanists and zoologists are agreed as to the 

 non-inheritance of changes which are induced by mutilation and disease. That 

 there isno direct evidence oi the inheritance of adaptations due to external factors, 

 was admitted above. The same is true of functional adaptations ; Vochting 

 (1899) has made many experiments on the subject and has established beyond 

 all question that such adaptations are not hereditary. The question comes to be, 

 whether any fundamental considerations can be advanced against the assumption 

 of their transmissibility. That would be the case if we conceived of the origin of 

 the adaptations in the individual as the zoologists often appear to do ; for they 

 assume that any alterations in the somatic-cells must be appreciated by the germ- 

 cells, but that can scarcely occur unless by a transference of idioplasm from the 

 somatic to the germ-cells. Such an assumption (Pangenesis, Darwin, 1868) 

 verges too near to empiricism, and it would appear to us that such an idea is 

 not only unessential for the explanation of the phenomena as presented by the 

 vegetable kingdom, but is in itself quite incorrect. Let us study a single example 

 of adaptation in the plant. If we place a land plant in water we do not find 

 that leaves already present change their shape and structure, but die off 

 just because they no longer possess the power of adapting themselves to 

 their new surroundings ; on the other hand, adaptations appear in the quite 

 embryonic leaf-initials, close to the growing point, where germ-plasm or idio- 

 plasm is much more abundant than in the full-grown parts. We find, that is to 

 say (and this is of general significance), that the adaptation does not take place 

 in the soma proper, but in the growing point. It is from the growing point, 

 however, that the reproductive cells are also derived, and they are able to receive 

 adaptive impressions without the inexplicable transference of a material basis 

 from the soma. Certainly we must assume the transference of a stimulus, inas- 



