THALLOPHYTES 



S. 



results in a filament of four cells, each of which gives rise to a slender 

 branch hearing a spore (fig. 194)- This saprophytic filament has been 

 called the promycclium, and its spores sporidut; 

 but it represents a four-celled basidium bearing 

 basidiospores, and is the structure that determines 

 the position of rusts among Basidiomycetes. 



Aecidiitm. — The basidiospores that fall upon 

 young barberry leaves germinate, and an extensive 

 mycelium is developed among the tissues of the 

 new host. This mycelium develops very evident 

 structures of two kinds. Opening usually upon 

 the upper surface of the leaf, small, flask-shaped 

 organs appear, known as spermogonia, within which 

 there arise slender filaments that form by succes- 

 sive abstractions numerous very small cells, the 

 spermatid (fig. 195). The names spermogonium 

 and spermatium indicate the belief that this struc- 

 ture is the male apparatus, to be compared with a 

 male conceptacle in Funis (see p. 50). However, 

 this function has not been demonstrated, and some 



regard them as spore-producing structures, in which 



. ] , ' , ... , . Fig. 194. — Wheat 



case they are spoken of as pycmdia producing rust . te leutospore P ro- 



pyCflidios pores. If this is ducingbasidia("promy- 



a' sexual apparatus, j t celia ") bearing basidio- 



spores ("spondia ). — 



would seem to be a ves- After tulasne. 

 tigial one. 



The other structure produced by the my- 

 celium in the barberry leaf is the aecidiitm or 

 dustercup. The aecidia usually appear in 

 groups on the lower leaf surface, each opening 

 upon the surface as a cup containing numer- 

 ous simple sporophores bearing rows of spores, 

 Fig. i 9S . — Wheat rust: & the aecidiospores (fig. 196). The scattered 

 spermogonium (producing aecidiospores that fall upon young wheat 

 spermatia) arising from the pl an ts germinate, the host is penetrated, and 



mycelium of the barberry leaf. fc ^j j 3 produced that begins to form 



— After Chamberlain. •> l ° 



uredospores. 



Polymorphism. — In this life history the fungus passes through 



three distinct phases (the parasitic mycelium bearing uredospores and 



