Damping Off, 313 



Resting Conidia. — These are conidia which do not germinate 

 immediately and acquire a somewhat thicker wall than the conidia. 

 They pass through a period of rest before germiiiating. They are 

 identical in form and size with the conidia. They are capable of 

 growing after being frozen, and after drying, and serve in this way 

 much the same function that the oospores do in that they tide the 

 fungus over quite long periods which are unfavorable for the growth 

 of the plant. 



In germination the conidium thrusts out, by an extension of its 

 wall, at one or more points, a slender tube which elongates into a 

 hypha exactly like those of the former mycelium. This enters a 

 young seedling when favorably situated, and starts the disease again. 



The conidia and zoospores are rarely developed so abundantly in 

 this species as are the oogonia. In my cultures during January and 

 February, 1894-5, the oogonia were far more abundant and no zoo- 

 sporangia were observed. DeBary says that sometimes one may 

 search for weeks and even months and not find zoosporangia. I 

 have, therefore, not had as yet an opportunity of studying the for- 

 mation of the zoospores from the zoosporangia and can not say 

 whether or not they agree with those of Artotrogus intei*medius 

 (deBary), which will be described in the next paragraph. The 

 following account is therefore abbreviated from published descrip- 

 tions.'' The zoosporangia are usually not to be differentiated from 

 the conidia until the time for the development of the zoospores. 

 They are either terminal or intercalary, and sometimes so much of 

 the protoplasm migrates into them during development from the 

 supporting hypha that this is emptied for a short distance near the 

 point where the wall separates the zoosporangium from the contents 

 of the hypha. They usually remain attached to the supporting 

 hypha and at the time of maturity, if placed in fresh water con- 

 taining oxygen, a short protuberance is developed on one side at 

 nearly right angles to the supporting hypha, which grows to a very 

 short tube of a varying length but always shorter than the diameter 

 of the zoosporangium. Into this tube the protoplasm migrates and 

 causes the end of the short tube to swell out into a rounded vesicle 

 of about the same diameter as that of the zoosporangium, with a 

 thin enclosing membrane. The protoplasm now breaks up into a 



3 DeBary, ZarKennt. d. Perouosporeen, Bot. Zeit. 39, 521, 1881,Beitr. z. Morph. 

 XI. Ph.vs. d. Pilze, IV, 1881. 



Subroeter, Pilze, in Eugler u. Pr.iutl, Naturl. Pflauzeafam. 1, 1 104. 



