﻿1903] OOGENESIS IN SAPROLEGNIA 237 



ter of the ^%%. It seems possible that Trow may have mistaken 



it at times for a centrally placed nucleus, to which it bears a ccr- 



J tain resemblance that might make the two structures indistin- 



I guishable in obscurely stained preparations. The coenocentrum 



does not appear until the processes of oogenesis are well under 



way. Previous to this period there are nuclear and cytoplasmic 



k activities of considerable import, and they will be considered 



, first. 



It is well known that with the flow of the protoplasm into the 

 I swollen tip of a hypha there is apparent that peculiar structure 



of the protoplasm {^fig. i), significant of its streaming movement. 

 The nuclei at that time are very small. When the oogonium is 

 cut off by a septum from the hypha that bears it, the protoplasm 

 becomes distributed almost homogeneously through the interior 



> 



(/<^- ^)- The nuclei then increase in size, -and shortly after show 

 most clearly that detail of structure that is to be expected in the 

 resting nucleus. This structure agrees with the accounts of Har- 

 per, Wager, Stevens, and myself for the nuclei in other types of 

 fungi, indicating that the conditions among these lower forms 

 are essentially similar to the nuclear structure of higher plants. As 

 IS shown In j^^5. J and ^, and especially in /^. d, there is a nuclear 

 membrane inclosing a well-differentiated nucleolus, prominent by 

 Its size and staining qualities. Much less conspicuous, but read- 

 ily demonstrated in well-fixed material, is a loose linin network 

 which contains the chromatic material. Trow's description of a 

 central body containing chromatin and nucleolar matter, but 

 " neither a nucleolus nor a chromosome," must have been founded 

 on inferior preparations. There are certainly no complexities in 

 Saprolegnia comparable to the so-called nucleolus of Spirogyra 

 (Mitzkewitsch, 189S, Wisselingh, 1900). 



There is one mitosis in the oogonium, but previous to that 

 event a number of vacuoles are developed which generally result 

 m a peripheral arrangement of the protoplasm around a large 

 central space or vacuole containing cell sap. The vacuoles 

 begin to appear immediately after the oogonium is cut off from 

 the parent hypha (/^. 2). They grow larger and run together 



{M- j) » until finally there are one 



or 



