506 H. MARSHALL WARD. 



spores, about thirty in number, were rolling over one another 

 and waving their cilia (fig. 26, d) still enveloped by the 

 vesicle of mucus, and by 11.37 they were fully formed very 

 active zoospores. At 11.43 the enveloping vesicle suddenly 

 gave way and the zoospores passed out free. Fig. 25 shows 

 drawings of the stage when the protoplasm, having all passed 

 out of the sporangium into the vesicular enlargement, is 

 writhing about in an amoeboid manner preparatory to its 

 simultaneous division into zoospores; a and b were drawn at 

 two successive minutes. These stages are between a and b of 

 fig. 26, which may now be described. 



The sudden "blowing out" of the hyaline dome into a 

 vesicle had just been completed at 11.40 (fig. 26, a), having 

 gone through the stages already described. Two minutes later 

 the writhing mass of protoplasm, having passed through the 

 stao-es figured in fig. 25, contracted towards the centre of the 

 swollen vesicle, and rapidly divided into about nine blocks (J), 

 which became separate amoeboid masses during the next three 

 minutes (c). At 11.50 — i.e., five minutes after — each mass 

 was an active reniform zoospore (Jj; at 11.52, the very 

 diffluent vesicle, having almost dissolved in the water, gave 

 way and allowed the zoospores (e) to escape. The complete 

 zoospore resembles those of the other species of Py thium in 

 its possession of a reniform amoeboid body, two lateral cilia 

 from the sinus, and a bright, vacuole-like spot near the base of 

 the cilia. 



In figs. 27 and 28 are shown the details observed as to the 

 germination of the zoospore after coming to rest. At a 

 (fig. 27) is drawn a zoospore actively moving at 5.15 in a very 

 minute drop of water. It was watched continuously, and drawn 

 again at 5.20 (i) and 5.30 (c), when it came to a standstill, and 

 commenced to withdraw its cilia. At 5.45 (d) the zoospore, 

 having come to rest, had lost its cilia and vacuole, and had 

 developed an envelope and several large refractive granules. 

 From this point, however, apparently owing to a want of oxygen 

 in the water, its changes were distinctly retrograde. At 

 6.5 (e) the granules were coarser, and at 6.35 (/) still larger. 



