180 THE LOWER FUNGI— PHYCOMYCETES 



5. Rhipidium Cornu (Bui. Soc. Bot. France, 18: 53, 1871). 



In this genus, the basal segment of the thallus is attached to 

 the substratum by rhizoids, and is often very irregular in form, 

 being variously lobed or branched (Fig. 68). The lobes in turn 

 give rise to numerous slender cylindrical branches which bear 

 the sporangia and sexual organs. These slender branches are 

 definitely constricted at their point of origin and elsewhere, 

 especially in connection with delimitation of the reproductive 

 cells. They may be sympodially branched below the originally 

 terminal sporangia. The form of the sporangium varies in the 

 different species from nearly spherical to long ellipsoidal, the 

 cell being always markedly broader than the hypha which bears 

 it. The zoospores pass from the sporangium into a thin-walled 

 vesicle which tends to elongate and become cylindrical before 

 rupturing. They are monoplanetic and reniform. The oogo- 

 nium is usually borne terminally and is fertilized by an anther- 

 idium applied near its base. The oospore is prominently areolate 

 at maturity. The genus contains at present four species, R. ameri- 

 canum Thaxter (1896: 320), R. thaxteri v. Minden (1912: 600), 

 R. europaeum (Cornu) v. Minden (1912: 597), and R. partheno- 

 sporum Kanouse (1927: 344). 



6. Mindeniella Kanouse (1927: 301). 



The basal segment or main axis of the thallus in this genus 

 is broadly club-shaped and essentially unbranched. Over its 

 broadened distal end sporangia and oogonia occur on short 

 pedicels. They are really sessile inasmuch as they are separated 

 from the basal segment only by a constriction closed by a cellulin 

 plug. The sporangium is large, pyriform to ovoid, and some- 

 times is ornamented with a circle of spines about the papilla 

 of dehiscence. The oogonia appear after the sporangia have 

 freed their zoospores. They are spherical, thick-walled, and 

 spiny over the entire surface. The oospore is spherical, smooth- 

 walled, and nearly fills the oogonium. Antheridia are unknown. 

 The genus was based on a single species, M. spinospora Kanouse, 

 and was referred by its author to the Blastocladiaceae. She 

 states that zoospore formation is "as in the genus Saprolegnia," 

 but does not say definitely that biciliate spores are formed. The 

 membranes are composed of true cellulose. Knowledge of the 

 genus is confined entirely to the original description and figures. 



