80 THE SAPROLEGNIACE^ OF THE UNITED STATES, 



finding its first swarming period suflficient, has dispensed with the more primitive 

 second one. 



Pringsheim states ('60) that the zoospores of Leptomitus lacteus germinate after 

 a single period of activity. I have seen, however, in pure cultures of this form, abun- 

 dant empty membranes with every appearance of having been cast ofl: by a diplanetic 

 zoospore (Fig, 118) ; but nnfortunately, I have not observed the actual escape of the 

 spores from them. 



After its final encystment the spore may germinate at once, if conditions are 

 favorable; or may remain for a short time capable of germination. In germination 

 the wall of the encysted spore grows out at one or more points into as many slender 

 tubes (Fig. 11, a-^), which may reach a length equal to several times the diameter 

 of the spore without nourishment. They soon exhaust the nourishment contained in 

 the spore, and, if more be not supplied, cease growing and die. If, on the other hand, 

 food is accessible, growth becomes more rapid and the tubes develop into vigorous 

 hyphse. At the very beginning of germination, the nearly spherical nucleus of the 

 spore takes a more elongate form and divides into two (Fig. 13) ; and by the repeated 

 bipartition of these nuclei and their descendants arise all the nuclei of the hyphse 

 derived from the spore. 



Some observations on the rate of growth of a germ tube of A'phanomyces sp. 

 may be worth lecording here. The tube was produced by a spore which remained 

 encysted in the head after all the rest had passed into the second swarming stage, 

 and was growing, therefore, without access to food (Fig. 11, a). At ten a.m. the 

 tube was just visible as a slight protuberance from the spore (Fig. 11, a); at 

 eleven it had reached a length of 37,a (Fig. 11, g) ; and at twelve it was 52,a long 

 (Fig. 11, i). The effect of the absence of a supply of food is plainly shown here. 

 While the growth during the first hour under the stimulus of the reserve materials 

 contained in the spore amounted to 35/y, that of the second hour, when this supply 

 was becoming exhausted, fell to 15^. 



We pass now to a comparison of the genera Thraustotheca, Dictyuchus and 

 jLplanes with those already described. It has been said that the zoospores of 8ap- 

 ?'o?e<7m'a and -4c/<?2/ct^ sometimes become encysted within the sporangium. This con- 

 dition is the normal one in the genei'a above named, but in these the development of a 

 mouth at the apex is wholly suppressed. In Thrausiotheca the entire wall of the 

 sporangium, except a narrow basal ring, breaks up after the encystment of the spores 

 and leaves them free or slightly held together by an intermediate substance. After 

 a time, they swarm in the laterally biciliate foi'm, encyst again, and germinate. The 

 sporangial wall o^ Dictyuchus^ on the contrary, does not break down, and the encysted 



