PH YCOM YCETO US A FFIXI TIES 



805 



This layer at maturity is split by cleavage planes to form many 

 small, prismatic, uninucleate segments lining the wall. These 

 may well be termed spore mother cells, for the nucleus in each 

 divides twice to give four, and four uninucleate spores round up 

 in each. Finally these spore tetrads break apart and the spores 

 recede from the periphery of the sac to become aggregated in a 

 ball near its tip. They are then ready for discharge. In 

 Taphridium essentially the same condition exists, except that the 

 spores are formed at the periphery of the chlamydospore before 



Fit;. 109. — (a) Protomyccs pachydcrmus Thi'iai. ( ■hhiniydosporc with extruded 

 sac-like endospore in section at stage when spore-mother cells line the sac. 

 (6) P. kriegerianus Biiren. Later stage; the spores aggregated in the apical 

 region of the extruded sac. (After Biiren 1915, 1922.) 



the extrusion of its endospore to form the sac. The two nuclear 

 divisions concerned in the formation of the spore tetrads 

 perhaps accomplish reduction but the point is as yet in doubt. 

 It is not certain, moreover, that nuclear fusion occurs in the 

 copulating spores. 



The genus Protomyces linger (1833) is the largest of the three 

 composing the family. Biiren (1915; 1922) gives a thorough 

 taxonomic treatment of its species for Switzerland. The type 

 species, P. macrosponis linger, is confined to the Umbelliferae, 

 but is composed of at least seven distinct biologic races. Ten or 

 more species occur on Compositae. Cytological conditions in 

 the genus have been studied chiefly in P. macrusporuH and P. 

 pachydermits. The cells of the mycelium are multinucleate. 

 The papers of Biiren (1913; 1914 a, h; 1915; 1922), Popta (1899), 



