7G MISSOURI BOTANICAL GARDEN. 



d 



isodiametric excepting the infected ones which are usually 

 elongated radially. The infected region, as shown in f. 14, 



located 



be 



to conditions in Ceanothus. Usually four to five layers of cells 

 outside of the central cylinder remain uninfected, although 

 there is some tendency for the fungus to penetrate inwardly. 

 Many cells are found which are just being infected quite near 

 to the vascular cylinder, butf in a young tubercle a compara- 

 tively thick layer of uninfected tissue remains outside of the 

 vascular cylinder. In a large mature tubercle the vascular 

 cylinder composes about one-fifth of the diameter and extends 

 quite far into the tip. It is quite uniform in width, except 

 that it tapers somewhat toward the end. Beside the endoder- 

 mis which surrounds it, the cylinder consists of a few strands 

 of xylem, still somewhat radially arranged, and with phloem 

 cells between them. The bundles are bounded bv narenchv- 



number 



the cylinder. 



A study of the developmental stages of the fungus may 

 best be made from a longitudinal section in which the various 

 stages can be determined. Beginning with the apex and con- 

 tinuing toward the base of the tubercle, serial stages may be 

 selected which represent the entire history of the fungus in 

 the various cells, the youngest stages being found in the grow- 

 ing region, whereas the oldest may be noted in cells at the 

 base of the tubercle. 



An uninfected host cell is usually isodiametric and con- 

 tains many large starch grains imbedded in a thin granular 

 cytoplasm. Occasionally a heavy staining substance is met 

 with which, however, has more of an intercellular than intra- 

 cellular appearance, and is much like the tannin met with in 

 the alder tubercles. The cell nucleus is relatively large and 

 filled with chromatin in a fine reticulated stage (f. 16, 17, 19) . 



Infection takes place acropetally; the fungus passes from 

 cell to cell by forcing its way through the cell wall (f. 16) 

 and frequently several hjrphae may be noted, placed along 

 the inside of the wall for a considerable distance before one 



