18 THE PHYCOMYCETES 



saprophytically on submerged plant materials, fruits of rose, 

 Crataegus, and tomato being especially preferred. Methods of 

 collection of these fungi and a taxonomic account of the genus 

 are given by Kanouse (1925, 1927). The thallus of Blastocladia 

 consists of a rhizoidal system within the substratum, from which 

 arises a main trunk or axis that branches repeatedly. At the ends 

 of the branches are borne the thin-walled sporangia which pro- 

 duce zoospores. The resistant sporangia are also produced 

 apically. Search for sexual reproduction in connection with 

 the s^ermination of the resistant sporangia has produced only 

 nes^ative results. The resistant sporangia of B. pringsheimii have 

 recently been germinated bv Blackwell (1940). She states that 

 after a rest period of several months they germinate, producing 

 zoospores which develop into asexual plants, just as do zoospores 

 from ordinary thin-walled sporangia. Thus sexuality is not 

 known in the Genus Blastocladia. 



The Genus AUomyces, recently monographed by Emerson 

 (1941), contains five species, all apparently of rather wide distri- 

 bution in soil. This extensive distribution in soil throughout 

 the world is stressed by Wolf (1939, 1941) and Emerson (1941), 

 but the function therein of these species is unknown, and no 

 one appears to have attempted to explain their wide dissemina- 

 tion. 



The structure of the thallus of AUomyces is quite similar to 

 that of Blastocladia. From the basal portion or trunk, attached 

 by rhizoids, arise numerous slender branches, which are separated 

 into segments by pseudosepta. On the branches are borne thin- 

 \\'alled zoosporangia and resistant sporangia similar to those of 

 Blastocladia. 



Interest attaches to two species of the genus, A. arbiisciila [But- 

 ler (1911)] and A. javamciis [Kniep (1929, 1930)], by reason 

 of the nature of their sexual reproduction and life cycle. In both 

 of these species there is a distinct morphological alternation of 

 sexual and asexual phases [Kniep (1930), Hatch (1935)]. On 

 germination of the resistant sporangia, the zoospores develop into 

 thalli bearing paired male and female gametangia. Both male 

 and female gametes are motile, the female being considerably the 

 larger and unpigmented, A\hereas the smaller gametangium is 

 orano-e in color. This pigmentation has been shown to be due to 

 the presence of y-carotene [Emerson and Fox (1940)]. The 



