CHYTRIDIALES 



105 



Clinton and Drechsler shows, moreover, a striking similarity in 

 morphology between species of the two genera. The presence 

 of the Sammclzellcn on the resting spores of these forms was 

 interpreted by Schroter as indicating a sexual conjugation of 

 young thalli, and he erected the genus Urophlydis to include 

 the sexual forms. This genus was incorporated by him in his 

 family Oochytriaceae, while the forms in which indications of 

 sexuality are absent were retained in Physoderma of the Cladochy- 



FlG. 37. — Urophlydis pluriannulatus (B. & C.) Farlow in Sanicula, except 

 (s) which is U. alfalfae (Lagerheim) Magnus, (h) Zone of haustoria. (m) 

 Secondary series of turbinate cells, (n) Young turbinate cells of tertiary series, 

 (r) Mature resting spore which arose as a terminal expansion of the apical 

 haustorium of turbinate cell (s) Mature resting spore bearing zone of pits mark- 

 ing points of disappearance of haustoria. (i) Septate turbinate cell whose cells 

 have put out hyphae bearing apically a secondary series of turbinate cells. 

 (After Jones and Drcchder 1920.) 



triaceae. His view was supported by investigations of Magnus 

 (1897; 1901 ; 1902) but has not been confirmed by others. There 

 seems to be at present no reason for believing that a sexual 

 process occurs in resting spore formation in any of the species. 

 Consequently, a new basis for separation of the genera Physo- 

 derma and Urophlydis has been sought, the one used here being 

 that suggested by von Minden. As here constituted, the genus 

 Physoderma includes those species which cause merely discolora- 

 tion or slight tliickening of the affected host parts, while Uro- 



