70 



MISSOURI BOTANICAL GARDEN. 



in other portions of the tubercle as well. From the infected 

 cells containing a mass of mycelial threads a stout hypha 

 passes out, dissolves its way through the cell wall, and passes 

 into the adjacent cell, directing itself toward the cell nucleus, 



om 



ing about it (f. 2). The infecting hypha is usually quite 



so than those of the much branched masses 



more 



(f. 3, 4), a provision evidently necessary because a delicate 



be 



readily, and even if it did, there would probably not be 



asm 



new host cell. 



At this early stage the mycelium is densely filled with 



_ a «■ 



r r mbedded 



ing very prominently with the haematoxylin stain although 

 the walls of the hyphae cannot be seen (f. 5, 6). After hav- 

 ing established itself, short branches originate from the first 

 hypha which in turn branch very abundantly and fill the 



greater part of the host cell (f. 4). 



When the fungus enters the cell there is a stimulation to 

 growth of the cell wall and the protoplast; adjacent unin- 

 fected cells are comparatively small (f. 8). The cytoplasm 

 increases and becomes densely aggregated about the nucleus 

 or about the fungal material, staining a very light orange, 

 producing a contrast between the cytoplasm of infected and 



uninfected cells. 



6 



abund 



ant in uninfected cells, have entirely disappeared and even 

 normal adjacent cells suffer the loss of their starch and 

 cytoplasmic content from the infection of their neighbors 

 (f. 2). The cell walls of the host are dissolved at quite an 

 early stage and often four or more cells break down, thus 

 increasing the space which the fungus ultimately fills. The 

 original content of such cells is absorbed very quickly. No 

 multinucleated cells are formed in this manner, but 



the nucleus of the cell in which infection originated grows 

 very rapidly with the fungus and remains the prominent part 

 of the host cell. The nuclei of the adjoining cells, which are 

 thus brought in contact with the infected cell, disintegrate 

 very readily, probably being used as food by the fungus. 





