FUNGI: THE RUST FUNGI 



281 



leaf. The hyphae of the outer layer are 

 sterile, and remain united laterally to form 

 the wall (peridium) of the cup, which is first 

 closed over the top but later opens out. 

 The cells of the central bundle of hyphae, 

 in chains, separate at maturity and form 

 the cluster-cup spores (aecidiospores). Upon 

 the upper side of the spot are much smaller, 



yellow, conical 

 elevations, seen 

 in cross section 

 at fig. 249. These 

 are the spermo- 

 gonia. They 

 produce numer- 

 ous very tiny, 

 rod - shape d 

 structures which 

 ooze out at the 



flask-shaped 

 spermogonia in a gelat- 

 inous mass, sweetish to 

 the taste. Fertilization 

 takes place by the fusion 

 of two cells in adjacent 

 rows at the bottom of the 

 young cluster cup in some 

 cases, and by the migra- 

 tion of a nucleus from a 

 basal cell into the one 

 above, or laterally situ- 

 ated in other cases. The 

 cluster-cup spores develop in chains from this, each having 

 two nuclei which do not fuse until the final stage of the life cycle 

 is reached in the tehutospore (paragraph 449). 



Figs. 245-247. 

 Fig. 245. 



Barberry leaf with two 

 diseased spots. Natural 

 size. 



Cluster-cup stage of wheat rust. 



Fig. 246. Fig. 247. 



Single spot, show- Two cluster 



ing cluster cups cups more en- 

 larged, showing 

 split margin. 



enlarged. 



Fig. 248. 



Section of an aecidium (cluster cup) from barberry 

 leaf. (After Marshall-Ward.) 



