188 ON THE SAPROLEGNIE^. 



The growth and development of Saproleg7iia takes place with 

 extraordinary rapidity. In thirty-six hours from the first infection 

 with the spores, a thick growth of the fungus has arisen, and by 

 the third day a thousand hyphae may have developed and emptied 

 their sporangia, setting free some twenty thousand zoospores, 

 each of which is competent to set up the same process afresh. 

 About the fourth day, the zoosporangia diminish in number, and 

 dictyosporangia make their appearance. In this form of sporan- 

 gium there is no exit for the spores. They encyst themselves, and 

 often germinate within the spore-case. Not unfrequently about 

 this time, the hyphae tend to break up into short joints, w^hich are 

 themselves capable of germination. 



After the sixth day, a new kind of sporangium makes its 

 appearance, which is termed an "Oosporangium," inasmuch as the 

 spores to which it gives rise are more like eggs or seeds than the 

 products of the other kinds of sporangia. The summit of a 

 hypha dilates into a spheroidal sac, the cellulose wall of which 

 becomes thickened, but presents here and there thin places, look- 

 ing like clear, circular dots or apertures under the microscope. 

 Protoplasm accumulates in the spheroidal case thus formed, and 

 either remains a single, rounded mass, or divides into a smaller or 

 greater number of spheroids, each of which, much larger than a 

 single zoospore, is termed an " oospore." About this time, 

 slender^ twig-like branches are given off, either from the stalk of 

 the oosporangium, or from an adjacent hypha, and the terminal 

 portion of one or more of these twigs applies itself to the oospo- 

 rangium. This terminal portion becomes shut off from the rest 

 of the twig by a transverse septum, and is an " Antheridium." 

 The antheridium pierces the wall of the oosporangium, at the 

 clear spots or apertures before mentioned, and divides into branch- 

 lets, which apply themselves to the oospores. Antherozoids then 

 pass from the antheridia into the oospores, and effect fecundation. 



Two other remarkable facts have still to be mentioned. In 

 the first place, that determined by Pringsheim — viz., that parthe- 

 nogenesis is not an uncommon phenomenon in Saprolegnia. 

 Some, or even all, of the oogonia on a plant may not be fertilised 

 at all, the formation of antheridia on them being altogether sup- 

 pressed ; nevertheless, the unfertilised oospores germinate, and 



