326 



THE FUNGI WHICH CAUSE PLANT DISEASE 



In a few species "*'' ^^ there are what are known as amphispores 

 or resting forms of urediniospores provided with thickened walls. 

 They have colorless contents and pedicels more persistent than 

 those of the usual urediniospore. 



III. Telia (teleuto-sori). Toward the latter part of the grow- 

 ing seasons another kind of spore appears, often in the same 

 sorus with the urediniospore and from 

 the same mycehum. It is of various 

 forms in different genera, one or more- 

 celled, varies in shape, thickness of 

 wall, surface marking, color, etc., but 

 is uniform in the character of the 

 germination which is very different from 

 that of any of the other rusl^spores. 



In teliospore germination, tjrpically 

 each cell of the teliospore sends forth 

 one germ tube. These tubes soon cease 

 growth and by septation become 4-celled. 

 Each cell then sends out a short branch 

 (sterigma) on which there develops one 

 round or oval, 1-celled, thin-walled spore, 

 the basidiospore, often in this group 

 called the sporidium. 



Morphologically the promycelium is a 

 basidium bearing its four sterigmata and 

 four basidiospores. Relationship is thus 

 shown on the one hand to the Ustilagi- 

 nales, on the other hand to the Auricula- 

 riales, an assumption that is borne out by cytological evidence. 

 Deviations from the typical mode of germination are found in sev- 

 eral genera mentioned belciw (e. g., Coleosporium). 



Basidiospores germinate immediately by germ tubes which on 

 suitable hosts give rise again to aecia and pycnia or in some 

 species to other spore forms completing the life cycle. 



The most complex life cycle is thus seen to comprise pycnio- 

 spores, seciospores, urediniospores, teliospores and basidiospores. 

 For brevity the first four stages are commonly designated by 

 the following sjTnbols: 



Fio. 240. — Germination of 

 teliospores of P. asparagi. 

 After Smith. 



