260 



FOUNDATIONS OF BOTANT 



red rust. A little later the black spores appear, produced from the 

 same mycelium. This growth is chiefly upon the stems and sheaths. 



A B 



Fig. 191. — Spore-Formation in Potato-Blight (Phytophtlwra in/estans). 



A, a well-developed group of stalks, proceeding from a mass of mycelium inside 

 the leaf and escaping through a stoma ; B, a young, unbf anched stalk. ^, 

 hyphae of mycelium ; o, stoma ; s, spore. (Both figures greatly magnified, B 

 more than A^ 



311. Cluster-Cup Stage. — Note with the naked eye and with a 

 magnifying glass the appearance of the cluster-cups upon the bar- 

 berry leaf. Fresh specimens should be used, if available. Note 

 whether the leaf is changed in form or color in any part occupied 

 by the fungus. Note the number of cups in a cluster, the position 

 on the leaf (which surface ?), the form and size, especially the height. 



