92 THE LESSON OF EVOLUTION 



not due to differences in temperature. Indeed the 

 fact that the most rapid movement is next to the 

 stationary layer is impossible to explain by the action 

 of any physical energy. In the hairs of the stamens 

 of another kind of plant called Tradescantia we see 

 threads of protoplasm crossing the cell cavity, and 

 in these the streaming movements are all directed 

 either from or to the nucleus. From this we con- 

 clude that the nucleus directs, and perhaps causes, 

 the movements. In Nitella chlorophyl granules are 

 formed in the stationary layer of the protoplasm. 

 The rotating protoplasm, however, gives rise to a 

 number of granules, formed of chromatin, which are 

 carried along passively in the current. 



The reproductive organs grow on the leaves. The 

 male organ, or antheridium, is formed from the ter- 

 minal segment of a leaf, while a pair of female 

 organs, called oogonia, grow from the lowest node 

 of the same leaf. These are complicated structures 

 which need not be described here. It is sufficient 

 to say that the antheridium gives rise to a number 

 of spirally-coiled antherozoids, which swim to the 

 oogonia and fertilise the single oosphere in each. 

 These now become oospores, and the cycle is com- 

 plete. 



These various operations occur over and over again 

 with the greatest regularity, even in the most minute 

 details into which botanists have been able to pene- 

 trate. Indeed we may feel sure that if the minute 

 details were irregular the results would be irregular 

 also. Still variations do arise, and it is to these that 

 we must now turn our attention. 



