INJURIES INDUCED BY PLANTS 153 



BASIDIOMYCETES 



The Bastdiomycetes constitute the third group of fungi. In 

 their case all spores originate by abscission. 



UREDINE.E.* RUST-FUNGI 



The rust-fungi are true parasites, and develop their mycelium, 

 which is usually intercellular, in the tissues of the leaves and 

 cortex (and also, though less frequently, in the wood, e.g. Cole- 

 osporium Senecionis] of phanerogams, and abstract their nutri- 

 ment by means of haustoria from the interior of the cells. 

 Their course of development is characterised by most species 

 producing sporocarps, which are usually cup-like in shape. The 

 bottom of these so-called aecidia is lined by a hymenium 

 consisting of numerous, usually club-shaped, basidia, each of 

 which at its apex abjoints a series of spores which are usually 

 reddish yellow in colour. These are united to each other by so- 

 called intermediate cells, which are dissolved before the forma- 

 tion of the spores is completed. The basidia that are situated 

 at the periphery of the hymenium, instead of forming spores, 

 grow together to form an envelope called the peridium, which 

 opens at the apex or by a longitudinal fissure. The peridium 

 may, however, be entirely absent. 



Before the formation of aecidia, spermogonia with spermatia 

 usually originate, the latter probably playing the part of male 

 sexual cells.-j- It is probable that the aecidium is the result of a 

 preceding sexual act, and is therefore a true sporocarp, like the 

 perithecium and apothecium of Ascomycetes. However, there 

 are also rust-fungi in which the aecidium is entirely absent 

 (Chrysomyxa Abietis). 



* [The British species have been worked up into a monograph by Plowright 

 (Brit. Uredinece and Ustilaginece, Kegan Paul, 1889), who has also devoted 

 attention to the experimental investigation of some of the hetercecious 

 forms. ED.] 



t [Researches into the morphology and physiology of these and other 

 organs of the Uredineae by no means support this conclusion. Brefeld's 

 statements, as well as those of De Bary, much as they differ in detail, point 

 to the opposite view that there is no probability of sexuality in this group. 

 The curious and interesting homologies are well put forth by Von Tavel.- 

 ED.] 



