PHYCOMYCETES 249 



enter a resting-stage and become clothed with a thick 

 wall. Such cysts are distinguished from zygospores by the 

 presence of well-developed, absorbing filaments, the homo- 

 geneous (not stratified) structure of the cell-wall, the 

 absence of a large oil-globule in the centre of the cell, and 

 by the existence of only one large nucleus, whereas zygo- 

 pores contain two nuclei. 



Protomyceteae 



The mycelium is intracellular, vaguely branched, septate, 

 producing numerous intercalary spores, after which it 

 disappears. Sporangia and zoospores unknown. Resting- 

 spores globose or broadly elliptical ; wall thick, consisting 

 of two or three layers. On germination the thin endospore 

 protrudes through a rupture in the thick wall of the resting- 

 spore as a sporangium, containing numerous minute, 

 cylindrical, motionless spores that conjugate in pairs. 

 After conjugation the spore emits a slender germ-tube 

 which enters the tissues of the host, where it forms a 

 mycelium which in turn produces resting-spores. 



The masses of resting-spores often form hard, warty 

 projections on the host-plant. Parasitic in the subepider- 

 mal tissues of flowering plants. 



There is a difference of opinion as to the relative value 

 of the present family. Its only genus, Protomyces, is 

 reduced to subgeneric rank, being included in Cladochy- 

 trium by Fischer. Brefeld includes Protornyces in the 

 Hemiascomycetes. 



Mucorineae 



The species are saprophytic, growing on decaying animal 

 or vegetable substances, ripe fruit, dung, etc. In some 



