110 Causes and Course of Organic Evolution 



lime that it is starting chemical changes in the contained sub- 

 stances of these cells. For such changes again, which involvt* 

 the liberation and action of ferments, we would suggest the 

 existence of a biotic energy. 



But it is when we study and experiment with dormant spores, 

 seeds, or tubers, and T\'ith cuttings, specially of a woody nature, 

 that highly suggestive confirmation of the existence of such 

 an energy is got. As for some protophytic plants, so for spores 

 and seeds, it has been shoTMi that many of these will live for 

 years in dormant state, if merely removed from normal water 

 supply. Similarly they can be exposed to decidedly high and 

 low temperatures. But here also a fairly, or even exactly, 

 definite time-interval is reached, when the protoplasmic mole- 

 cules begin to disrupt and death ensues. 



If it be here asked why some seeds, e. g., those of Gram- 

 inacese, retain vitality only for one to five years, those of 

 Malvaceae for five to ten years, and those of some Legum- 

 inosse for ten to seventy -five years, this seems in part to be 

 due to the nature of the reserve food, but is probably in large 

 measure due to the intimate relation of the embryo proper to 

 its large food-storing cotyledons, in which, apart from the 

 stored starch and protein, there is a large amount relatively 

 of protoplasm in the Leguminosse. On the other hand, in 

 Graminacese research has shoT\ii that much of the starch may 

 be stored in cells devoid of protoplasm, while those seeds in 

 general wliich show short vitality have the embryo and stored 

 food as separate structures. 



The spores of many fungi are known to have a high tem- 

 perature-resistance and age-resistance. Thus yeast according 

 to A. Mayer continued to bud up to 53° C. and when air-dried 

 its cells will survive after heating to 100° C. Cells of pressed 

 yeast, at oi)timum temperature, will remain alive for two 

 years. The stored energy of such minute cells must be great 

 and of a perfect quality, to permit of survival for so long a 

 period. 



The possibilities for survival of woody cuttings or shoots, 

 and of the aerial parts of desert ic plants such as cacti, euphor- 



