PUCCINIA 233 



ing of a single palisade layer, and five or six irregular layers of 

 spongy parenchyma. 



2. That the greater bulk of the infected part is due not 

 so much to increased number of the cells as to the larger size of 

 the individual cells and of the intercellular spaces. 



In the sections prepared with chlor-zinc-iodine, if a good 

 staining has been effected, note with a low power that the 

 fungal tissues are but slightly stained yellow, while the tissues 

 of the host are stained in the usual way, chiefly a dark blue. 

 Recognize as the most prominent parts of the parasite 



1. The secidia, cup-like structures, containing a closely 

 packed mass of spores, and opening by rupture through the 

 lower epidermis of the host. 



2. The spermogonia, relatively small, flask-shaped organs 

 opening on the upper surface of the leaf. 



Having thus gained a general idea of the sections, examine 

 them in detail under a high power, and note that in the infected 

 patch the cells of the host are apparently embedded in a felt of 

 mycelium, consisting of septate and branched hyphse, which 

 traverse and completely choke up the intercellular spaces : they 

 are but slightly stained with chlor-zinc-iodine, while the cell- 

 walls of the host plant assume a dark colour : they are for the 

 most part confined to the intercellular spaces, and especially 

 those round about the aecidia ; but it is stated that occasionally 

 they penetrate the cells of the host, and though this is not easy 

 to see, examples of it should be looked for. Turning to the 

 aecidium observe 



1. Its cup-like form. 



2. The dense felt of hyphae at the base of it. 



3. Immediately above this is the hymenium, a layer com- 

 posed of closely packed, parallel, rod-like cells (basidia), 

 arranged perpendicularly to the outer surface of the leaf. 



4. The rows of spores, which have been successively ab- 

 stricted from the basidia : observe the hexagonal form, thickened 

 wall, and orange colour of the spores, and the way in which the 

 spores of contiguous rows fit together. 



5. The peridium, consisting of a single layer of cells en- 

 veloping the mass of spores : the form and arrangement of the 



