JoB.^fiO^—^Ohri/sophli/ctis endohiotica mid other Chijlridiacece. 135 



absorbed by aud reappear in part in the individual developing zoospores. 

 When looking for sprouting sporangia, I had an experience one day 

 (20tliNov., 1908)of sufSciently general interest to deserve a detailed account. 

 1 saw several zoosjJores rushing very rapidly backwards and forwards through 

 the field of the microscope. I found next an elliptical sporangium with a 

 small hole in its wall at one end. The sporangium was practically full of 

 zoospores swarming most vigorously and crowded round the opening in the 

 wall in what looked like a general wild rush to be amongst the first to escape 

 into the fresh air dissolved in the surrounding water. Within a minute the 

 sporangium was emptied. The motion of the zoospores through the field of 

 the microscope was comparable to that of a mouse in a room ; and the rough 

 analogy is not lessened by the fact that the pear-shaped zoospore moved with 

 its single cilium behind. Some of the zoospores were caught between the 

 glass-slide and cover-slip and became stationary. Tiie body of the zoospore 

 (1'5-2'4|U in diameter) was actively amoeboid, going through changes of form 

 too rapid for me to sketch in succession (PI. XI., fig. 6). The cilium remained 

 either straight or became curved like a carriage-whip, and usually moved 

 passively with the body of the zoospore, though it also showed slow sweeping 

 movements backwards and forwards. Suddenly the body would be seized 

 with a violent spasmodic fit, shake itself free (or not) from its temporary 

 imprisonment, and swim away. The amoebidity of the body of the zoospore 

 and comparative passivity of the cilium were striking. 



My letter to Nature in November, 1908, announcing the observation of 

 the multisporous character and the germination of the resting sporangia, 

 called forth a letter from E. F. Weiss recording his observations of germinat- 

 ing spores in August. The time of the year suggests that these must have 

 been the summer ones whose germination Schilberszky had already described. 

 The resting ones do not, in ray experience, germinate with ease in potato-juice, 

 as Weiss found his sporangia to do. If they had done so, I sliould not have 

 spent three months in examining them day by day under various conditions. 



Marchal had the same difficulty witii the resting spores of the Chytridian 

 Asterocystis radicis. He saw the escape of the zoospores from the summer 

 sporangia readily, but failed to make the resting ones germinate, though he 

 found them from time to time in his cultures ruptured and empty. Tliis is 

 equally true of the resting spores of Olpidmm brassicae, the cause of " black 

 leg " in young cabbages. It looks as if, judging from Chrysophlyctis, rest- 

 ing spores must be cultivated in a decoction of or in immediate contact with 

 the host-plant, that its chemotactic influence may be exercised on them to 

 arouse the zoospores to activity. Summer sporangia sprout without diffi- 

 culty in water material in most Chytridiaus. 



