Pethybridge — Observations on Phytophthora erythrose'ptica. 185 



certainty in any given case until they are liberated. At this stage the 

 contents are slightly contracted from the walls, more particularly at the 

 apex. Figs. 5 and 7, on Plate XIII, show zoosporangia in this condition, 

 although the amount of contraction shown in fig. 5 is somewhat exaggerated 

 owing to fixation with iodine and subsequent mounting in dilute glycerine. 



The apical, thicker, and more hyaline portion of the sporangium-wall now 

 begins to bulge rapidly outwards, becoming extremely thin as it stretches, and 

 quickly assumes a more or less spherical form, sometimes almost equal in size 

 to the sporangium itself. Practically simultaneously with this bulging of 

 the wall, the mass of zoospores passes out, filling this bladder-like swelling, 

 the extremely attenuated wall of which at once dissolves. The zoospores 

 then disentangle themselves from one another, and swim actively away. 



At times, however, the liberation of the zoospores is not so rapid, possibly 

 because the place of exit is relatively narrower. The apical portion of the 

 wall swells up, and becomes dissolved; and through the opening, the zoospores 

 squeeze out more leisurely, separating from one another, as a rule, imme- 

 diately on reaching the exterior. Not infrequently some of the zoospores 

 remain behind in the sporangium, and ultimately produce germ-tubes in 

 situ. Cases have also been observed in which the zoospores seem reluctant to 

 leave the sporangium. One or two of them may get out, do not swim far 

 away, and soon produce germ-tubes. The majority of them remain behind, 

 more or less rounded off within the sporangium. A case of this kind is 

 illustrated in fig. 8, Plate XIII. 



The number of zoospores in each sporangium varies eonsiderablj', and is 

 dependent on its size ; numbers varying from eight to twenty-three have 

 been observed as they leave the sporangium. 



The shape of the zoospores is on the whole oval, and more or less bluntly 

 pointed at one or both ends ; but during the period of motility their shape is 

 constantly changing. Sometimes zoospores possess more or less of a tail, 

 which may be rather short and blunt, or nearly as long as the chief portion 

 of the zoospore itself. In the latter case it often resembles a fine thread, 

 with small portions of protoplasm attached to it at intervals. 



Apart from these " tails," which are not of very frequent occurrence, each 

 zoospore possesses two cilia, one being about twice and the other about three 

 times as long as the zoospore. There is also in each zoospore a vacuole and a 

 bright spot. In addition to this, when in active motion a darkish longitu- 

 dinal line or groove appears to be present ; but its nature, owing to the 

 rapidity of motion, could not be determined with accuracy, and it disappears 

 as soon as the movements begin to slow down and the zoospores come 

 to rest. The cilia are not easily seen when the zoospore is at its height of 



