﻿1903] OOGENESIS IN SAPROLEGNIA 243 



Saprolegnia are too small to present conspicuous morphological 

 evidence of this character ; but we have the fact that the favored 

 nucleus is almost always pressed against the coenocentrum which, 

 together with the appearance of the nuclei and what we know of 

 . ,_ the events in Albugo, makes it quite certain that the coenocen- 



trum exerts a chemotactic influence. 



The changes that come over the ^^^ as it matures are iUus- 

 trated mjif^s. 16-21, which show the usual uninucleate condition 



of the ^gg. Binucleate and trinucleate eggs will be described 



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in the following paragraphs. The two most important events of 

 maturation are the increase in size of the nucleus and the gradual 

 dissolution and final disappearance of the coenocentrum. The 

 growth of the nucleus involves not only the extent of the space 

 inclosed in the nuclear membrane {figs. 17-21), but also means 

 a great increase in the amount of staining material, chromatic 

 and nucleolar. The latter must be very many times greater in 

 quantity in old eggs than at the beginning of oogenesis (compare 

 fig^ 16 \v\i\ifigs. 20 and 21). The coencentrum decreases in size 

 until it becomes a very small globule [fig. 20), or it may split up 

 into several granules, which soon become lost in an ill-defined 

 mass of denser protoplasm. The coenocentrum finally disappears, 

 and the contents of the ^gg then arrange themselves around a 

 central vacuole, with the nucleus taking a peripheral position. 

 This is the structure of the mature e^r^:, and is illustrated in 



fig- 2T. 



We will now consider some conditions that have given rise to 

 much discussion, namely, the binucleate and trinucleate eggs. 

 They have been found by Humphrey, Hartog, and Trow, and 

 ^ the present study indicates that they may be expected in any 

 member of the Saprolegniales. Trow attached much significance 

 to them as evidence of sexuality, but his conclusions seem to 

 the writer open to much criticism and will be taken up later. 

 Pigs. 22-2S illustrate several conditions that show how easily an 

 ^%% may become binucleate. Suppose two nuclei lie near enough 

 to the coenocentrum to share about equally the advantages of 

 position. Then it is not likely that either will give way to the 

 other. Such conditions in a young ^<y% are shown in/>. 22, 



