DA.MI'INCi OFF Fr.NGL'S AM) ALLIED FORMS. 237 



zoospores [Fiii". 11], or of giving off vegetative- tubes which grow 

 very rapidly. [Fig- !-•] lu the former case the regular process of 

 zoospore foniiation seems to be taken up just where it was inter- 

 rupted, passing through the "partial segregation" (spore-origin) 

 stage, the "homogeneous" stage, and finally the protoplasm separat- 

 ing again, — this time permauentW — forming zoospores. When the 

 tubes are formed instead, they ma}' spring from any portion of the 

 sporangium, usually one to each. The parietal protoplasm of the 

 zousporangium occupies a similar position in the germinal tube, the 

 lumen of the latter being continuous with the cavity of the former. 

 [Fig. 18.] 



A physiological consideration of the resting zoosporangia is 

 interesting in showing the conditions under which they are formed, 

 and taken in connection with their structure may show their origin, 

 use, and homology. In my cultures of Saprolegnia monoica I used 

 mosquitoes as a substratum, as they were of convenient size and 

 seemed to furnish sufficient nourishment for a complete generation 

 of the fungus, without offering extra material to decay and attract 

 bacteria. After getting cultures started I secured new ones by 

 transferring escaping zoospores only, thus being enabled to obtain, 

 asexually, generation after generation of the plant. My observa- 

 tions in this particular do not accord with the statement of Hartog, 

 that "on the whole it appears that cultures from successive genera- 

 tions of zoospores tend to produce oospores more readily." On 

 the contrary, I found that, after ten "or fifteen generations of 

 zocisporic reproduction, there Avas a decided diminution in the num- 

 ber of oosporangia formed, as well as in the number of oospores 

 which they contained. In addition to this there was manifestly a 

 tendency toward the disappearance of the antheridia even when 

 oogouia were produced. Finally there was a total cessation in the 

 production of oogonia, and only resting zoosporangia with two or 

 three enlargements appeared. The disappearance of the oogonia 

 and antheridia, and the decrease in the number of oospores point 

 to a deterioration of the fungus. 



The formation of the resting sporangium at such a time must be 

 interpreted as an attempt on the part of the plant to produce 

 something of a reproductive nature longer-lived than the very 

 transient zoospores, after it becomes too degenerate to produce 

 ■oospores. Practically the same features were observed in experi- 



