1914] COULTER—REPRODUCTION IN PLANTS 345 



of the primitive gametes are no essential part of a sexual cell. The 

 need for emphasizing this is apparent when it is realized that this 

 secondary feature of a sperm has been regarded as its essential 

 feature by those who demand rigid categories. When motile 



* 



sperms were first discovered among gymnosperms, they were hailed 



as the only sperms in seed plants. In other words, the sperms of 



most seed plants were not regarded as sperms because they cannot 

 swim . 



Another rigid conception in reference to the sperms of angio- 

 sperms needs attention. Ciliated sperms are produced and dis- 

 charged by the mother cell. This has led to so rigid a definition of 

 a sperm that if the sperm generation is omitted it is concluded that 

 there are no sperms. The usual formula for describing this sit- 

 uation has been to say that "the mother cell functions directly 

 as a sperm," implying that in fact there is no sperm, but that the 

 mother cell behaves like one. Since the test of a gamete through 

 all its history is its behavior, it is difficult to understand such a 

 statement, except that a secondary feature has been substituted 

 for the essential one. It is obvious that if organization and dis- 

 charge of a sperm by a mother cell are essential to secure freedom 

 of approach to the tgg, when another method of approach is secured, 

 the necessity for discharge disappears. The protoplast within the 

 mother cell and the discharged sperm are the same protoplast. 

 The sperm mother cell of angiosperms behaves like a sperm because 

 it is a sperm. 



The obvious conclusion is that a sperm is a protoplast which 

 fuses with another one to form a zygote; that in visible features it 

 differs originally in no essential way from any other protoplast; 

 that eventually it becomes less bulky than its mate on account of a 

 difference in the amount of cytoplasm; that it often develops an 

 elaborate swimming mechanism as a secondary feature; and that 

 the swimming apparatus is eliminated when the necessity for 

 swimming disappears. 



The phenomenon of "double fertilization" in angiosperms 

 introduces a situation that is suggestive. In this case a sperm 

 fuses with another cell, so that there is the same mutual attraction 

 as between egg and sperm, leading to contact and fusion, but there 



