114 THE SAPROLEGNIACEJE OP THE UNITED STATES, 



tyuclms sp. The other was freshly collected and gave also A. cornuta, A. mega- 

 sperma, and 8. torulosa. 



I have not followed the zoospore from its encystment to its germination; but, 

 as the spores germinate freely in cultures which contain no trace of empty mem- 

 branes, such as are seen with germinating diplanetic spores, there can be no doubt 

 of their monoplanetism. The general appearance of the plant and of its sporangia 

 strongly suggests a JPythium, as intimated in the generic name. The formation of 

 the zoospores does not appear to follow the course above described as characteristic 

 of the family. I have not been able to study the process in detail, but it seems to 

 be much simpler than that usual among Sapr'olegmacece. While the escape-papilla 

 may appear more than three hours before the exit of the spores, no change is evident 

 in the protoplasm of the sporangium until fifteen or twenty minutes before that 

 event. The separation of the spores within the sporangium is very slight and I 

 have seen nothing corresponding to the two separation stages, with an inteimediate 

 stage of swelling up. One might regard this as leading towards the simpler zoo- 

 spore formation of the Peronosporece, but for the fact that the zoospores are terminally, 

 and not laterally, biciliate. The whole question deserves careful comparative study. 



The outgrowths of the oogonial wall are only exceptionally rather long ; and in the 

 great majority of cases are not at all developed. In a very large number of oogonia 

 examined, I have seen only one (Fig. 67) with more than a single oospore. DeBary 

 states that three sometimes occur. He also mentions the presence of as many as 

 four antheridia on an oogonium. Amherst specimens have rarely had more than 

 one each and never more than two. I have seen, also, the peculiar hyaline outer 

 layer surrounding some oogonia, which was mentioned by DeBary ; but cannot 

 regard it as due to an extrusion of periplasm, as is suggested in his account ('88), 

 since no periplasm is observed in other oogonia, and because it may occur on young 

 oogonia before the formation of the oosphere, as well as on adult ones. I am, how- 

 ever, quite unable to explain its origin. On young oogonia it appears to be thicker 

 than on older ones, but it has been seen at all in my cultures only exceptionally. 



Achlya Nees ab Esenb. ('23). 



Syn.: Byssus aquatica Fl. Dan. (1780). Exsic: Algues de la France, 238 {A. prolifera). 



Vaucheria aquatica Lyngb. ('19). Rabh., Algen Sachsens, 242 {do.). 



Hydronema Carus ('23). 

 Leptomitns prolifer Ag. ('24). 

 Saprolegnia capiUdifera Braun ('51). 



Hyphae usually stout, sometimes slender. Zoosporangia formed from their 



