Formation of Tcleutosporcs of Ustilaginco'. 69 



Localisation of Spore-beds. — The bulk of the Ustilagineae 

 are characterized by the constancy by which they repro- 

 duce their spore-formation, in the same tissues of their 

 respective host-plants. In the majority of the species the 

 spores are localized somewhere in the reproductive organs 

 of the host-plant ; very frequently in the ovary {Tillctia 

 tritici, decipiens, U. caricis, Thecaphora hyalind), or in the 

 anthers {U. violacea, scabioscB) ; often the blossoming and 

 fructifying organs are attacked and destroyed {U. segetum^ 

 bromivora, kiihneana, SpJiacdothccd) ; sometimes the leaves 

 are affected (JJ. longissima, T. striceformis, Uroc. ocadta), or 

 the stems {U. hypodytes, grandis), or even the subterranean 

 organs {U. hypogcea, Uroc. gladioli^. With Entyloma and 

 its allies, however, this selection of tissue by the parasite 

 does not obtain ; with these species the spore-formation 

 seems to occur in almost any part of the plant. 



Structure of the Teleiitospores. — The teleutospores of 

 the Ustilagineae consist of two membranes: an outer, which 

 is thick and generally dark-coloured — the exospore ; and 

 an inner, which is thin and hyaline — the endospore. The 

 exospore is subject to considerable variety; it may be 

 quite smooth, or covered with extensive reticulations. 

 Between these various intermediate conditions occur ; thus 

 in U. segetiim it has generally been regarded as smooth, 

 but it is rather to be described as granular, although Winter 

 speaks of it as being " generally very minutely verrucose, 

 and seldom quite smooth." The degree of roughness of 

 the epispore varies from extremely minute elevated points 

 to marked tubercles. These elevations may be evenly 

 distributed over the whole spore, or they may be confluent 

 in lines or ridges. Sometimes these ridges anastomose, 

 and so form a reticulate or alveolate spore {T. tritici, 

 Sphacelotheca). The colour of the spore depends upon that 

 of the exospore ; as a general rule the spores, as seen 



