76 ZOOLOGY 



in this than in the more common event. As so often 

 happens when we study life, we find that it is the com- 

 monplace, the everyday thing, which is most marvelous. 

 So careful is Nature, in the majority of cases, to bring 

 about cross-fertilization, to unite diverse individuals in 

 the stream of inheritance, that innumerable adaptations 

 have arisen to that end. Thus many flowers, although 

 producing both ovules and pollen, do not ripen both at 

 the same time, or have special structures to bring about 

 cross-fertilization through the agency of insects. In the 

 common garden sunflower, although the pollen of any 

 head falls all over the adjacent stigmas, it is quite inert, 

 and no seeds are produced unless pollen is brought from 

 another plant. 



Fertilization 8. From Dr. Loeb's experiments with the sperm of 

 process 6 unrelated animals we gather this, that what we ordi- 

 narily call fertilization is a double process. It is, first 

 of all, the initiation or liberation of the activities of the 

 egg cell, and secondly the union of the nuclei with their 

 chromosomes. The latter has to do with heredity, the 

 former not at all. The wrong kind of sperm may serve 

 as a fertilizer in the sense of starting development, be- 

 cause the chemical substances it carries are adequate 

 for that purpose ; but its chromosomes are too different 

 from those of the egg cell to unite with them to make 

 an organism. Many different machines may be run by 

 the same power, but the parts of those machines cannot 

 be mixed up and transposed without stopping all pro- 

 duction. 



