330 UREDINEAE. 



geniiiuatiou they behave more like typical teleutospores than 

 aecidiospores. 



Before the relationship of these various forms of spores was 

 known, Aecidium and Caeoma were regarded as independent 

 groups, and named as such ; even yet many isolated forms of 

 uredosporcs, teleutospores, and aecidiospores are known, the 

 relationships of which are quite obscure. 



The aecidia are always preceded or accompanied by a further 

 form of spore produced in a special structure of its own. These 

 spores have hitherto been called spermatia, and their sporocarps 

 spermogonia, on the assumption that they were male organs. 

 Now, however, many of them are known to be capable of 

 germination in artificial nutritive solutions, hence they are more 

 probably a form of asexual bud, and better named conidia, 

 their sporocarps pycnidia. The pycnidia are tlask-shaped 

 structures sunk in the tissue of the host, with a pore or 

 mouth emerging through the host-epidermis ; they generally 

 occur in leaves, and occupy the upper epidermis, the aecidia 

 occurring on the lower. From the mouth of the pycnidium 

 there frequently emerges a tuft of fine filaments, outgrowths 

 from the inner wall of the flask. The pycnidia possess a lively 

 colour and flowery odour, hence it has been suggested that 

 the conidia may be distributed by insects; but they do not 

 appear to be able to germinate in the open, and infection- 

 experiments with them have never as yet succeeded. On this 

 account they are regarded as degenerate structures.^ 



The various forms of spores are also distinguishable by the 

 manner in which they bring about infection. Teleutospores on 

 germination produce sporidia, which pierce the membranes of the 

 prospective host at a spot where two adjoining cells are in 

 contact, and thus make their way into the intercellular spaces. 

 Uredospores and aecidiospores, however, first seek a stoma and 

 enter the intercellular spaces of the host through it. 



The following different forms of Uredineae exist : (1) Those 

 which possess teleutospores alone, e.g. Chrysomyxa alietis ; (2) 

 those with teleutospores and uredospores, e.g. Fuecinia 2^'^'uni 

 sinnosac ; (3) those with all the forms of spores, e.g. Puccinia 

 graminis ; (4) those without uredospores, e.g. Gymnosporangium. 



'Rathay, " Untersuchungen iiber die Spermogonien d. Rostpilze," Diitksrhri/t 

 d. Wiener Akad. d. Wissennch., 1883. 



