GROUP I. THALLOPHYTA : FUNGI. 



PhytopJtthora omnivora infects and destroys the seedlings of the Beech and 

 other plants. In Cystopus (C. Candidas on Capsella and other Crucifers, 

 C. cubicus on Compositse) sporophores bearing numerous sporangia are 

 formed in great numbers close together under the epidermis, and 

 cause its rupture. 



Order 2. Saprolegniaceae. The Saprolegniacese all live in water, and 

 are mostly saprophytic, though some are parasitic ; one species causes the 

 Salmon-disease. 



Asexual reproduction is effected entirely 

 by zoospores ; they are formed in terminal 

 but not otherwise especially differentiated 

 sporangia (Fig. 169). On coming to rest 

 they germinate to form a mycelium. They 

 are, in some forms, surrounded by a thin 

 cell-wall at their first formation. 



The oogonia and pollinodia (when pre- 

 sent) resemble those of the Peronosporaceae. 

 The number of oospheres in the oogonium 

 varies widely in different individuals ; 

 sometimes there is only one (Leptolegnia, 

 Aphanomyces) ; but as a rule there are 

 many, as many as 30-40 ; in either case 

 they are developed from the whole of the 

 protoplasm of the oogonium. 



The male and female sexual organs are 

 commonly borne on the same hypha, but 

 in some cases (e.g. Saproleynia dioica and 

 anisospora) this is not the case ; however, it 

 is not clear that these species are actually 

 dioecious. In some species (Saprolegnia 

 Thureti, (orulosa, monilifera, and Achlya 

 stellata) no male organs are developed as a 

 rule; in others (Saprolegnia mixta, Achlya 

 spinosa) they are as often absent as present ; 

 in others they are frequently absent 

 (Aphanomyces stellatus, Saprolegnia hypogyna, 

 Aplanes BrauniY); in others, finally, they 

 are always present (Achlya racemosa and 

 polyandra, Saprolegnia monoica). 



When pollinodia are present, they are 

 closely applied to the oogonium ; sometimes 

 several are applied to one oogonium. In 

 some forms (e.g. Saprolegnia asterophora) the 

 pollinodium undergoes no change, or it 

 sends out a short tube which enters the oogonium but does not touch the 

 oospheres. In most others the pollinodium sends out one or more tubes 

 which enter the oogonium and come into close contact with the oospheres. 

 But in all cases the tubes remain closed, and no act of fertilisation has 

 M.B. U 



FIG. 169. Zooeporangmm of 

 an Achlya : A closed ; B the zoo- 

 spores are escaping ; c a lateral 

 branch ; a zoospores just escaped ; 

 b empty membranes ; e swarming 

 zoospores. ( x 550 : after Sachs. ) 



