590 THE AMERICAX XA I L RALIST. [\ ni.. XX.WI 1 1. 



which will be given a separate treatment in this section. The 

 coenogamete is the homologue of a nniltinucleate gametangium 

 but its evolutionar)^ tendencies seem to be towards such a 

 reduction in the number of nuclei that in the highest expression 

 of Its sexual differentiation the female cell contains a single 

 nucleus and has the general form of an egg. But this process 

 of sexual evolution is entirely independent of the well known 

 lines of development in the Algae (Davis, Popular Science Monthly, 

 Feb. 1903). The female sexual cell of the Ascomycetes (called 

 the ascogonium or archicarp) is probably in most forms the 

 homologue of a gametangium. These subjects will be treated 

 in our account of the coenogamete. 



The egg in the archegonium of bryophytes and pteridophytes 

 is generally reported to have a clearer region on the side nearest 

 the neck and this is called the receptive spot. It is reported 

 by Campbell in his investigations on Pilularia ('88), Isoetes ('91), 

 Osmunda ('92a), Marsilia ('92b), and Marattia ('94), by Shaw in 

 Onoclea ('98) by Thom in Aspidium and Adiantum ('99) and 

 by Lyon in Selaginella (: 01). The receptive spot is generally 

 believed to be a portion of the egg differentiated to receive the 

 sperm. It is an open question whether this area is morpholog- 

 ically the homologue of the receptive spot in the eggs of algae 

 and the clear area at the ciliated end of motile gametes and 

 zoospores. The problem demands a detailed study of the finer 

 protoplasmic structure to determine whether or not it is kino- 

 plasmic in character. The nucleus is generally situated near the 

 center of the egg and the portions of the cell farthest away 

 from the neck of the archegonium contain coarsely granulate 

 protoplasm which is evidently trophoplasmic, /. e., much of its 

 substance is of the nature of food material and the products of 

 metabolism. The leucoplasts would be supposed to lie in this 

 region of the cell but we know nothing of their presence and 

 behavior in the egg of bryophytes and pteridophytes. 



The eggs of gymnosperms generally speaking present sharp 

 contrasts to those of pteridophytes. They are very large, prob- 

 ably the largest uninucleate cells in the plant kingdom, and 

 consequently very attractive for cell studies and some of the best 

 work on the events of the maturation and fertilization of plant 



