10 PLANT PHYSIOLOGY 



tions, it is not in all cases essential to the preservation 

 of life. 



The vital functions may be suspended, without deterio- 

 ration of the germinating power of the resting body, for 

 periods varying with the species and in some instances 

 astonishingly long. As a matter of safety, the dry seed or 

 spore should regularly retain its vitality at least for some- 

 what longer than the usual period during which, by reason 

 of heat, or cold, or drought, active life is impossible. Some 

 seeds may retain their germinating power for much longer 

 times, during which all activities are practically suspended. 

 The majority of authentic cases of suspended activity indi- 

 cate that beyond thirty years exceedingly few seeds remain 

 alive. It is probable that during these periods of appar- 

 ently suspended activity, some of the vital processes still go 

 on, so slowly as to be unnoticeable, but resulting ultimately 

 in the consumption or destruction of essential constituents 

 of actively living protoplasm. Seeds which have lain dor- 

 mant too long have, therefore, lost essential constituents; 

 their actively living protoplasm cannot be reconstructed 

 when water is added ; they have lost their power of germi- 

 nation. 



The survival of successive periods of drought by certain 

 species of mosses, liverworts, lichens, algae, and bacteria in 

 their vegetative instead of spore forms is even more remark- 

 able. The spores and seeds which survive periods of inac- 

 tion have at all times few functions to perform. The vege- 

 tative forms of mosses, liverworts, lichens, algse, and bac- 

 teria have to perform, or to prepare for, all the functions 

 of these organisms. It is all the more remarkable, there- 

 fore, when they are regularly able to survive, though all 

 their vital functions may be suspended. This implies a con- 

 siderably greater power of endurance than is possessed by 

 the vegetative parts of more highly organized plants. Yet 

 in California, and in other parts of the world, where there 

 are several months in each year when no rain falls, though 

 in other months it falls abundantly, plants growing in un- 

 cultivated places must be able to adjust themselves to the 

 periods of enforced inaction. So far as our Pacific Coast 



