. The fungi which cause plant disease . Plant diseases; Fungi. 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-
. The fungi which cause plant disease . Plant diseases; Fungi. 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
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectfungi, bookyear1913
