HEMIBASIDIOMYCETES 321 



Uredin-aceae, are seen in Doassansta, where the clusters of 

 spores are enclosed in a peridium of closely packed, dark 

 coloured, sterile cells arranged in a single layer. In 

 Sphacelotheca hydropiperis^ which invests the ovary of 

 Polygonum hydroptper, the sporophore is more complex, 

 being furnished with a thick outer wall and a central axis 

 or columella, the spores being produced in the cavity 

 between the two. The spores described above are resting- 

 spores, or chlamydospores of Brefeld, germinating after a 

 period of rest. Aecidia are unknown. Conidia are pre- 

 sent in the genera Entyloma and Tuberrinia, appearing as 

 delicate white mould-like patches on the living leaves of 

 the host-plant. 



The first product of germination of a resting-spore is a 

 germ-tube of limited growth, the promycelium, which soon 

 bears small secondary spores. A remarkable feature about 

 these secondary spores is that they usually conjugate in 

 pairs ; that is, adjacent pairs become organically connected 

 by a short tube growing from one and fusing with the 

 other. In some instances, as in Tilletia, this fusing occurs 

 before the secondary spores break away from > their point of 

 origin. After conjugation a slender germ-tube is formed 

 which receives the protoplasm from both secondary spores, 

 and if situated on a suitable host, penetrates the tissue and 

 forms a mycelium. In some species the germ-tubes arising 

 from the conjugation of two secondary spores produce 

 tertiary spores ; these in turn produce germ-tubes capable 

 of infection. The above mode of germination occurs 

 when resting-spores germinate in water, but Brefeld has 

 shown that when placed in a nutrient solution the results 

 are quite different. Instead of giving origin to a promy- 

 celium of limited length, the germ-tube continues to grow 



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