308 



PART III. THE CLASSIFICATION OP PLANTS. 



myxa, the teleutogonidia germinate, producing sporidium-bearing promycelia, 

 as soon as they are ripe and before they have fallen off (Fig. 217). 



In addition to the fructifications already described, there is a form, known 

 as Ctfoma, about which there is some uncertainty as to whether it represents a 

 sorus of uredogonidia or an secidium ; in some cases it appears certainly to be 

 the latter. 



Besides the genera enumerated above, the life-history of which has been 

 more or less investigated, there are a number of Uredo- and .ZEcidium-forms, as 

 well as most Ceeoma-forms, the connexion of which has not yet been ascer- 

 tained. These are, for the present, simply designated Uredo, JScidium, Caeoma, 

 constituting temporary form-genera. 



The list on p. 309 illustrates the life-history and heteroecism of the principal 

 genera. 



Order 2. Ustilagineae. This order comprises those parasites which are 

 known as Smuts. The life-history of most of the members of this order, is 



briefly as follows. The plant produces 

 numerous thick-walled, often black (Smut) 

 resting-gonidia, the development of which 

 is usually intercalary (resembling that of 

 chlamydogonidia) on more or less special- 

 ised mycelial branches (gonidiophores). 

 On germination, the resting- gonidium 

 forms a number of reproductive cells, 

 sporidia, of various form ; the sporidia 

 are usually developed on a small pro- 

 mycelium, which may be either multi- 

 cellular (Fig. 218 A), or unicellular (Fig. 

 218 B) but in one genus, Protomyces, 

 they are developed inside the resting- 

 gonidium, which acts as a gonidangium, 

 the only instance of the kind in the 

 ^Ecidiomycetes. In most forms these 

 sporidia then coalesce in pairs ; but in 

 any case they germinate, either producing 

 at once the mycelium which will bear the 

 resting-gonidia (e.g. Protomyces), or a 

 second promycelium bearing secondary 

 sporidia, from which the mycelium bearing resting-gonidia is developed (e.g. 

 Tilletia Caries). 



In some species (e.g. Entyloma Ranunculi, Tuburcinia Trientalis) the myce- 

 lium, before it produces the resting-gonidia, developes another kind of gonidia ; 

 these are small, thin-walled, somewhat spindle-shaped cells, developed by ab- 

 striction from the ends of unbranched simple gonidiophores. 



The sporidia, when cultivated in nutrient solutions, maybe made to multiply 

 actively by gemmation, producing a number of yeast-like cells. 



With regard to the life-history of the order, it may be pointed out, in the first 

 place, that the resting-gonidia correspond to the teleutogonidia of the Uredinea3 ; 

 secondly, that the sporidia in the two orders correspond ; and lastly, that the 



4. 



Jt. 



FIG. 218. Germinating reating-goni- 

 dia : A of Ustilago receptaculorum ; B of 

 Tilletia Canes ( x 460) : sp the gonidium ; 

 pm the promycelium; d the spondia : 

 in B the sporidia have coalesced in 

 pairs at v. 



