28o Journal of Agricultural Research voi. iv, no. 4 



considerable numbers on string-bean agar. The normal life history, 

 however, can be observed only under aquatic conditions. Cultures upon 

 sugar-beet seedlings in water in Petri dishes where abundant aeration 

 was obtained have been employed in the studies discussed in this paper. 



A profuse, hyaline, nonseptate, branching mycelium with a finely gran- 

 ular internal structure develops (PI. XLIV, fig. 12). The young hyphae 

 vary from 2.8 to 7.3/t in width, while portions of threads destined to 

 function in reproduction may considerably exceed that diameter. Cul- 

 tures I or 2 days old which have been well aerated at favorable (warm) 

 temperatures exhibit remarkable protoplasmic streamings which, so far 

 as they have been obser\^ed, are always directed toward the distal ends 

 of the hyphae. At such times the protoplasmic granules, or mitochon- 

 dria, to which attention will be directed presently, may be seen to change 

 their relative positions constantly and to exhibit a more or less inde- 

 pendent motion. This protoplasmic streaming leads to an accumulation 

 of material in the extremities of the threads, in consequence of which 

 they become enlarged and more or less distorted according to the condi- 

 tions. At length a partition wall is laid down to cut off the swollen 

 portion from the rest of the myceHum; thus the first step in the process 

 of fructification is accomplished (PI. XLIV, fig. 7). 



The body thus cut off merits special attention. It is similar in general 

 appearance to the zoosporangia of various types which develop in the 

 Saproligneaceae ; but a study of its function shows that it differs dis- 

 tinctly from them, since it gives rise, not to zoospores, but to the body 

 in which the zoospores are formed. While closely related in origin 

 and appearance to the sporangium, it is correlated with important modi- 

 fications in the process of zoogenesis which have not previously been 

 described and constitutes a special organ with a new and sufficiently 

 differentiated function to justify its designation by a distinctive name. 

 The term " presporangium " is therefore applied to it. When fully 

 formed, this body varies greatly in size and shape, depending upon the 

 point where the cross wall is laid down. The presporangium may vary 

 in length from less than 50 to more than i ,ooo;(. The width may scarcely 

 exceed that of undifferentiated hyphae, or it may increase to 20/z. Branch- 

 ing is present or absent according to the character of the segmented 

 portion of the hypha before metamorphosis. After being cut off, these 

 bodies increase in diameter, taking on a distinctly swollen and more or 

 less distorted appearance. This step is accomplished apparently by 

 taking up water which accumulates in vacuoles (Pi. XLIV, fig. 13, and 

 PI. XLVIII, fig. i). The consequent development of turgor eventually 

 becomes great enough to rupture the wall of the presporangium and 

 permit the discharge of its contents, which emerge in an uncleaved condi- 

 tion (PI. XLIV, fig. 6, 10). The rupture usually occurs at the extreme 

 end of the hypha, though it sometimes takes place at the tip of one of 



