352 LECTURE XXI. 



at least, by a not too excessive drying-up. Numerous experiments with Algae and 

 Fungi show that by means of desiccation (which must not be carried too far however) 

 the dormant period can be shortened in many cases, and some observations not yet 

 sufficiently confirmed allow of the conclusion that even in the winter-buds of trees 

 something of the same kind occurs. But in all cases where the resting spores, or in 

 Phanerogams the seeds, as those of Trapa, go through their dormant period at 

 the bottom of deep water, we cannot speak of the co-operation of desiccation. All 

 this appears to indicate rather that in every case it depends upon chemical changes 

 in the dormant parts of the plant ; changes which proceed only extremely slowly, and 

 generally require months for their completion. These chemical changes do not 

 affect the proper reserve-materials as such, however, or at least not throughout their 

 mass, as follows from the fact that in potato tubers, which have been so very 

 frequently investigated, no striking difference has ever yet been found in the 

 chemical composition in the autumn, before the dormant period, and in the spring 

 following it. In the same way the numerous observers have perceived no changes 

 which immediately affect the reserve-materials in the Algae and Fungi. 



On the contrary, all vigorous chemical changes only appear at the commence- 

 ment of germination, and we know already that these changes of the reserve- 

 materials are in great part effected by means of ferments. From these considera- 

 tions I come to the conclusion that, in the case of dormant periods, it may be a 

 matter of a very slow production of ferments, which are formed in the buds capable of 

 growth; and that the possibility of putting the existing reserve-materials into the active 

 state in which they are directly suitable for the requirements of growth, only appears 

 when they have been produced in sufficient quantity. That this production of 

 ferments may be in its turn favoured by various external circumstances during the 

 dormant periods — e. g. in many cases by desiccation or the cold of winter — is not to 

 be denied. On the other hand, in cases where spores, buds, tubers, and seeds are 

 capable of germination immediately after their production, it may be assumed that 

 they take up the necessary quantity of ferments or similarly effective matters at the 

 time of their origin, from the mother-plant. 



Since at the present time the attention of vegetable physiologists is being 

 directed towards ferments, it is to be hoped that researches will not be wanting to 

 confirm or contradict the hypothesis here put forth. In any case the periodic 

 alternation of rest and vegetative activity, as one of the most general phenomena in 

 the life of the plant, is worthy of greater attention than has hitherto been accorded 

 to it ^ 



' Pfeffer has collected the literature on the annual periods of vegetation in his ' PJlanzcn- 

 physiologie' pp. io6, &c. 



