2i8 A TEXTBOOK OF THEORETICAL BOTANY 



Monoblepharis 



It is not proposed to describe in detail any one species, since none is 

 relatively more common than the others and there are differences in the 

 sexual reproduction features which make a single description incomplete. 



Until quite recently species of Monoblepharis were regarded as extremely 

 rare Fungi and little was known about their life-histories. From the time 

 when they were first described by Cornu over seventy years ago particular 

 interest has attached to them because they are the only oogamous Fungi 

 known in which a motile male gamete is employed. Recent work on the 

 group has shown that the reason for their apparent scarcity was primarily 

 a matter of understanding the rather peculiar requirements necessary for their 

 active growth, without which they are usually swamped by more vigorous 

 members of the Saprolegniaceae. It is desirable here briefly to indicate these 

 conditions. 



The Fungus favours the shallower parts of fresh-water ponds and ditches 

 which are not liable to disturbance, resulting in the deposition of silt. Many 

 and various are the submerged twigs upon which the Fungus will grow, and 

 the host plant appears to have little influence upon the growth of Mono- 

 blepharis. When collected such twigs are not likely to show any obvious 

 signs of the presence of the Fungus, but after being washed in water in the 

 laboratory they are placed in glass jars filled half-full of sterile water. The 

 jars are then placed for several weeks in a refrigerator working a few degrees 

 above freezing-point, at the end of which time a copious growth of the 

 Fungus may be expected. 



From this fact it may be deduced that the Fungus grows best during the 

 autumn months when the temperature is low and when other aquatic Fungi 

 are less vigorous, and passes the spring and summer in a resting condition, 

 probably in the form of the oospores. 



On a well-infected tw'ig the mycelium will appear pale grey in colour, 

 forming a tuft of hyphae about 2 mm. in length. These hyphae are easily 

 recognizable by the regular vacuolation of the protoplasm which gives the 

 coenocytes a net-like appearance. Branching is monopodial and occurs 

 rarely. 



Asexual Reproduction 



Under favourable conditions, that is between 8^ and 12° C, asexual 

 reproduction occurs. The zoosporangia arise as slightly swollen terminal 

 portions of hyphae (Fig. 209). They possess at first a homogeneous cytoplasm 

 and many nuclei, and are separated from the rest of the hypha by a septum. 

 By means of cleavage furrows the contents become divided up into 

 uninucleated zoospores. The apex of the zoosporangium dissolves away and 

 the spores creep out by amoeboid movement. These zoospores, even at this 

 stage, possess a single flagellum, three or four times as long as the diameter 

 of the spores, and either immediately, or after a period of amoeboid 



