THE FUNGI WHICH CAUSE PLANT DISEASE 301 



The chlamydospores may be simple or compound, fertile or in 

 part sterile and are variously shaped and marked as described in 

 the genera below. 



The chlamydospores may germinate at once or after a more or 

 less protracted rest interval. In germination in water or nutrient 

 solution (manure water, etc.) a short tube is protruded, the pro- 

 mycelium, this differing in character in the two families, Figs. 217, 

 231. From the promycelium of most species there develop conidia, 

 (often called sporidia) 1-12 or even more. The promyceUum is 

 regarded as homologous with the basidium of the other basidio- 

 mycetes and the conidia as basidiospores. 



The conidia in suitable nutrient solutions often undergo repeated 

 and indefinite budding closely simulating yeast cells in appearance. 

 Fusion of conidia is not uncommon. 

 Fig. 218. Conidia finding lodgment 

 in suitable plant parts under suitable 

 environmental conditions give rise to 

 infection. The points at which in- 

 fection can occur are very diverse 

 with different species and will be 

 considered under the separate species 

 below. 



The vegetative cells are binucleate 

 in Tilletia, multinucleate in the Usti- 

 laginacese.^'^'' The young chlamydo- 

 spores were shown by Dangeard ^'"^ in the case of Doassansia, 

 Entyloma, Ustilago and Urocystis to be binucleate. These two 

 nuclei, according to Dangeard, later fuse rendering the mature 

 spore uninucleate. In geririination the one nucleus passes into 

 the promycelium, then divides mitotically Fig. 217, 2. A second 

 division gives four nuclei (Fig. 217, 5) the spore nuclei.* 



In the fusions of smut conidia Federly has found an accom- 

 panying nuclear fusion, in salsify smut, while Lutman finds similar 

 fusion in the conjugating promycelial cells of oat smut.^ 



Whether or not these nuclear fusions represent a sexual act is 

 a much controverted point. 



There are according to Clinton about four hundred species in 

 America.*' ^* 



Fig. 218. — Ustilago. 17, conidia 

 fusing; 19, promycelial cells 

 with fusion tube, apical cell dis- 

 organizing. After Harper. 



