210 



THE LOWER FUNGI— PHYCOMYCETES 



prominent wart-like or sac-like protuberances which give it a 

 striking appearance. The oospore is thin-walled. Its method 

 of germination is unknown. The asexual stage as described is 

 unlike that of any other member of the order. Hyphae form a 

 subiculum beneath the epidermis of the host from which a dense 

 mass of sporangiophores arises. The epidermis is ruptured and 

 mealy masses of sporangia are formed on the surface of the host. 

 The sporangiophore is variable in form. In its simplest type it is 

 merely an erect hypha terminated by a single sporangium. The 

 tip of the sporangiophore is usually enlarged, however, to form 



Fig. 74.^ — Trachysphaera fructigcna Tabor & Bunting, (a) Sporangiophore 

 with swollen vesicle (1) bearing a whorl of spherical cchinulate sporangia and 

 two other vesicles (2 and 3) which have not yet borne sporangia, {b) Rough- 

 walled oogonium accompanied by an amphigynous antheridium. (c) Oogonium 

 and oospore in longitudinal section. (After Tabor and Bmiting 1923.) 



a more or less globose vesicle from which a number of sterigmata 

 arise, each terminated by a sporangium. Some of the sterigmata 

 may grow farther and form other vesicles bearing additional 

 sporangia. The sporangia ("conidia") are spherical, strikingly 

 echinulate, and germinate by germ tubes. 



The presence here of the amphigynous type of antheridium, 

 hitherto known only in Phytophthora, gives the genus unusual 

 interest. This is especially true in view of the fact that the 

 asexual stage is unhke that of other members of the Oomycetes 

 and recalls that of certain of the Mucorales. The proper position 

 of the genus in the classification is perhaps in doubt. 



Peronosporaceae 



Mycehum intercellular in higher plants; haustoria developed 

 and variously shaped in different genera; sporangiophores definite 



