PLANT RHYTHM 117 



The effect of the moon on plants has been clironiclcd much 

 more rarely, but there is a common alga known as Didijota 

 which in one part of the world produces its sexual cells once 

 in each lunar month, and in other parts of the world twice 

 a month. 



Certain flowering plants are said to bend their stem towards 

 the moon and follow its course by night as it moves on its 

 fixed path. The effect of the seasons on many perennial 

 plants is too well known to need much comment. They burst 

 into life as spring comes on, live throughout the summer, and 

 their visible parts disappear with the autumn, though tucked 

 away underground is a remnant capable of reproducing the 

 plant at the return of spring. 



This season's Daffodil, 



She never hears. 

 What change, what chance, what chill, 



Cut down last year's : 

 But with bold countenance. 



And knowledge small, 

 Esteems her seven days' continuance 



To be perpetual. 



KiPLiNO, Cities and Thrones and Powers. 



The climatic changes in the tropics are at a minimum both 

 in the hot, damp forests and on the desert tracts of Africa, 

 Asia and America. The changes of season are but very slightly 

 marked. Hence the activities of plants and animals proceed 

 all the year round without the interruptions caused by the 

 hot and cold seasons of more temperate zones. Trees in the 

 tropics make no annual growth-rings. Nevertheless there is 

 a periodicity, a rhythmic alternation of periods of repose and 

 activity. Certain plants and animals as a whole show little 

 of this periodicity, but even these have resting periods for 

 certain of their functions. The less the periodicity of the 

 climate is, the less is the plant dependent on it, and such 

 alternations of rest and activity in a uniform climate are in 

 the main due to internal causes. In the densest and most 

 humid tropical forests there is a time for breeding and a time 

 for vegetative recovery. But this may not affect all the plants 

 of one species at the same time, and hence one finds that a 

 given species is in bloom for long periods of time even during 



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