RHYTHMS IN PLANT LIFE 61 



there shall be a period of vegetative growth, or asexual 

 reproduction, or sexual reproduction. As Pfeffer says : 

 " In Algae, the stimulation is usually due to such factors as 

 light, water, or temperature, and a regular alternation of 

 generations would be maintained by a constant periodicity 

 of the climatic factors." In the higher plants, as in the 

 higher animals, there seems to be a relatively greater freedom 

 from the direct grip of the environment, and the altered 

 conditions which bring about flowering, for instance, may be 

 of internal origin, that is to say, not in direct dependence on 

 the march of the seasons or any other external periodicity. 

 Keeping in mind this general idea of internal rhythm and 

 external punctuation, let us think of some of the fundamental 

 facts of plant life in spring. 



GERMINATION 



Increasing warmth, more light, softer winds, and 

 Spring showers these are some of the familiar physical 

 conditions of the universal reawakening in Spring. Were 

 we wise enough we should be able to trace the whole chain of 

 causes the long succession of stimuli which connects the 

 increased share of the sun's energy with the germination of 

 seeds, the ascent of sap, the unpacking of buds, the return of 

 the migrants, the rise of song in the bird's throat, the awake- 

 ning of the sleepers, the emergence of the butterfly from 

 the chrysalis, the quickening of the pulse in man. " Our 

 very hearts have caught the charm that sheds a beauty 

 over earth." 



Let us first think for a little of the germination of seeds. 

 Among plants, as among animals, one of the lines of evolu- 

 tion which is discernible is that which leads to prolonged 

 connection between the mother organism and its offspring. 

 In a seaweed, for instance, what leaves the parent organism 



