1920] WILSON— CROWN-GALL 



55 



Just before the exit of the zoospores a motion of the sporange 

 contents is visible. The fatty globules are jostled about although 

 they do not flow together. In a spore which is not viable the fat 

 is frequently congregated into one or two large drops, but such 

 a spore was never seen to develop into a sporange. The motion 

 within the sporange is followed by the rupture or dissolution of 

 I the inner wall layer, allowing the zoospores to escape through the 



J openings in the outer layer. The difficulty of observing their 



I direct exit is enhanced by the fact that the porous side of the spo- 



range wall is almost always downward in the hanging drop. The 

 I zoospores escape sometimes in groups, but usually singly. Often 



they seem to have difficulty in locating the pores, and they may 

 swim about in the sporange for a considerable time or even dis- 

 integrate there (fig. 19). Atkinson (i) has observed an interesting 

 amoeboid movement of zoospores within the sporanges of Rhi- 

 zophidium globosum just previous to their escape. Although no 

 such amoeboid movements were seen at this stage in my material, 

 the alternation of resting and active periods is a common occur- 

 rence, just as was observed by Atkinson. 



In stained sections the development of the sporanges may, be 

 traced in a fairly complete series. Even in the very early stages 

 each nucleus seems to be related to a definite portion of the cyto- 

 plasm (fig. 26). The nuclei have never been observed to occur 

 in groups, but are rather uniformly distributed. As development 

 continues, the nuclei decrease in number, as shown by the number 

 present in a cross-section of a sporange. Apparently there is a 

 disintegration of many of the small nuclei, while those which are 

 to take part in the formation of zoospores increase in size. The 

 structure of the latter nuclei also becomes much more clearly dif- 

 ferentiated, and they stain with more uniformity (figs. 20, 27). 

 The chromatin is now aggregated in knots connected by slender 

 threads (fig. 16). In most of the preparations the connecting 

 threads are not easily seen; in such cases one or more knots are 

 apparent just within the nuclear membrane (figs. 20, 27); these 

 large nuclei are the centers of zoospore formation. Barrett (4) 

 found in Olpidiopsis nuclei similar to those here described, which 

 served as centers of zoospore formation. The transition stages 



