ANGIOSPERMS 445 



it had no special function, save possibly to be of service 

 in case anything happened to its mate. 



But a few years ago a surprising discovery was made. 

 It was discovered that this second sperm moves on into 

 the embryo-sac. It reaches that pair of nuclei at just 

 about the time that they are beginning to fuse to form the 

 endosperm-nucleus, and it joins in their fusion. In other 

 words, the endosperm-nucleus is the result of the fusion 

 of three nuclei, a triple fusion. Thus we have what is 

 described as double fertilization, — one sperm contribut- 

 ing to the formation of the embryo, the other to the forma- 

 tion of the endosperm. 



It is hard to explain this double fertilization. There is 

 nothing to explain it by. Nothing has been discovered 

 among the lower plants which throws any light upon the 

 evolution of this habit. So far as we know it originated 

 among angiosperms themselves. It is one of the many 

 unexplained things in plant life. 



A plain illustration of the effects of double fertihzation 

 is found in corn. Here we find characters of the pollen 

 parent appearing in the endosperm as well as in the em- 

 bryo, which seems natural enough now that we understand 

 how to explain it. Have you ever noticed red kernels in 

 a white ear of corn? It is not uncommon to find them, 

 and double fertilization explains how they happen. It is 

 presumed that the pollen whose sperms reached these red 

 kernels came from a plant with a tendency to produce red 

 ears. It is the endosperm which is red. Now that we 

 know that one of the sperms fuses with the endosperm- 

 nucleus, we can readily see why the quality of redness 

 which comes from the pollen parent may, appear in the 

 endosperm. 



