186 Scientific Proceedings^ Royal Dublin Society. 



activity ; indeed under these conditions it is extremely rare to see the one 

 directed forward in the line of progression, possibly on account of its rapid 

 movements. The one directed backwards, however, is more easily seen, and 

 appears to act as a kind of rudder. 



Attempts to fix the zoospores satisfactorily when in a motile condition 

 with the vapours of osmic acid, formalin, and chloroform, as well as with 

 iodine solution, failed. These substances cause the zoospore to become 

 shattered, leaving a mass of small granules in a hyaline matrix of irregularly 

 rounded shape, larger than the living zoospore, without vacuole or bright 

 spot, but with the cilia still present. The same thing occurs when a beam 

 of sunlight is caused to fall on the zoospores by means of the sub-stage 

 mirror of the microscope, just as they are leaving the sporangium. 



The maximum and minimum periods of motility have not been deter- 

 mined ; but in many cases, after swimming about for from twenty minutes to 

 half an hour, the motion becomes more sluggish. The zoospore itself 

 generally remains almost stationary, becomes nearly spherical in sliape, and 

 slowly lashes its two cilia. Soon all movement ceases, and a completely 

 stationary spherical body results. For a few minutes longer the cilia can still 

 be seen, after which tliey gradually fade from view, apparently becoming 

 dissolved, and not witlidrawn into the interior. It is at this stage that it can 

 most clearly be seen that the two cilia have a common point of origin, or 

 nearly so. As the cilia fade away the outline of the spore becomes more and 

 more clearly defined, owing to the formation of a definite wall. 



In this condition the spores have a diameter varying from 8(U to lift, the 

 average being about ll/z. After a further period of an hour or two, each 

 spore sends out a delicate germ-tube, into which the contents pass, leaving 

 the spore empty and sometimes cut off from the germ-tube by a transverse 

 wall, formed at some little distance from the spore. Germinated zoospores 

 are illustrated in fig. 8, Plate XIII. 



II. Micro-Chemical Reactions of the Walls of the Sexual Organs 

 AND Germination of the Oospores. 



For a detailed account of the peculiar method of development of the 

 sexual organs reference should be made to the paper already quoted. 



When the oospores are ripe the hyphae bearing the oogonium and the 

 antheridium respectively, as well as the antheridium itself, are practically 

 devoid of contents. The funnel-shaped base of the oogonium is clearly seen 

 within the antheridium, and is closed by a thick hyaline plug. 



The ripe oospore with its thick wall may or may not completely fill the 



