306 



PART III. THE CLASSIFICATION OF PLANTS. 



surface to set free the spores. The spores are conveyed by the wind to Grass- 

 ., plants, on the leaves of which they germinate, putting out hyphee which 

 penetrate into the interior through the stomata, giving rise to the mycelium 

 which bears the uredogonidia, and subsequently the teleutogonidia. 



On the assumption (see p. 279) that the aecidium, like the ascocarp of the 

 Ascomycetes, represents the sporophyte in the life-history of these plants, all 

 the other forms of the plant are stages in the life-history of the gametophyte, 

 namely the Uredo-form, the promycelium, the 2Ecidium-form. Of these, the 

 two former are altogether asexual ; the form bearing the eeeidium, by analogy 

 with the sexual Ascomycetes, represents the actual gametophyte; but although 

 the sterigmata in the spermogonia may, by analogy with some of the Ascomy- 

 cetes, be regarded as male organs, and the spermatia as male cells, no female 

 organ, corresponding to the archicarp, has yet been discovered. 



The following species have essentially the same life-history as that described 



above, though the host-plants are 

 different in all cases ; the species 

 of Heteruromyces, such as Uro- 

 myces Poce, U. Dactylidis, U. 

 Junci, U. Pisi, etc. ; the species 

 of Heteropuccinia, to which 

 group Puccinia Graminis belongs, 

 such as P. coronata, P. sessilis, 

 P. Eubigo-vera, P. Caricis, etc. ; 

 the species of Eucoleosporium, 

 such as Coleosporium Senecionis ; 

 the species of Euchrysornyxa, 

 such as Chrysomyxa Rhododen- 

 dri, C. Ledi. 



The following are the more 

 important variations on the life- 

 history given above : 



a. The Uredo-form is absent. 

 In the Endophyllese the secidio- 

 spore gives rise, on germination, 

 to a promycelium, which pro- 

 duces sporidia (as described 

 above) ; the sporidium gives rise 

 to a mycelium bearing aecidia. 



b. The Uredo-form only pro- 



FIG. 216. Transverse section of a Willow-leaf 

 infested by Melampsora salicina : par mesophyll 

 of leaf; eo upper, eu lower epidermis. On the 

 under side a sorus of uredogonidia (st) with 

 paraphyses (p) has broken through the epi- 

 dermis; beneath the upper epidermis is a sorus 

 of young teleutogonidia (t). (x 260.) 



duces teleutog&nidia, otherwise the life-history is the same as that of Puccinia 

 Graminis (e.g. Gymnosporangium). 



c. The JZcidium-form is absent; the Uredo-form produces only teleutogonidia : 

 here the only forms are the Uredo-form bearing teleutogonidia, and the pro- 

 mycelium bearing sporidia, which give rise to the Uredo-form on germination 

 (e.g. species of Puccinia [Leptopuccinia] such as P. Malvacearum, P. Arena.ria>, 

 P. Circ<z<z). 



d. There are no distinct Uredo-forms and JEcidium- forms : the same mycelium 

 gives rise first to secidia and then to teleutogonidia (e.g. species of Uromy- 



