124 PLANT PHYSIOLOGY 



colouring matters and of producing spores, and this loss of power has become 

 hereditary, i. e. many generations of cells, increasing vegetatively, have, in spite 

 of normal culture conditions, failed to regain the capacities mentioned. The 

 characteristic point in this process is the gradual fixation of the loss of power ; 

 for at temperatures of definite height the formation of spores ceases at once, 

 but on cooling it recommences, and it is only after long-continued exposure 

 to high temperature that a permanently asporous race is produced. Should 

 the loss of capacity be actually final a point as yet requiring proof the 

 question would be whether it might not be that in this case a mutation had 

 appeared better adapted to the unsuitable environment, and which had, for that 

 reason, killed out the original forms. It is possible, however, that the loss of 

 capacity is still not absolutely final, but that it lasts longer than the operating 

 cause of loss. We know indeed of changes in the plant of which this is true, 

 and in speaking of periodicity we got to know of so-called ' after-effects ' 

 which it is possible to correlate with the after-effects of a high temperature as 

 affecting loss of spore-forming capacity. 



If in these and similar cases we have to deal with heredity in the true 

 sense of the term, then we would have before us cases of what the zoologist 

 terms ' inheritance of acquired characters '. WEISMANN (1892) attempted to 

 show that the inheritance of such characters is theoretically impossible, and 

 that it has never been proved in practice. 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 peculiari- 

 ties 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. 



That the majority of such reactions do not make themselves evident in 

 the offspring under normal conditions is self -apparent. If an organism became 

 deformed by injury or by a parasite, and if that deformation reappeared in 

 the offspring without any injury or the presence of any fungal parasite, its 

 reappearance would be indeed extraordinary. On the same supposition we 

 would expect the offspring of plants grown in shade to exhibit ' shade-leaves ' 

 when grown in light. 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 vege- 

 table 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-primordia, close to the growing point, where germ-plasm or idioplasm 

 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 adaptative impressions without the inexplicable transference of a 

 material basis from the soma. Certainly we must assume the transference of 



