FUNGOUS ROOT-TUBEKCLES. 



85 



large and simple, but occasionally compound grains may be 

 found in the older cells. The cell nucleus is spherical in 

 shape and relatively small compared with the size of the 

 cell (f. 30). The chromatin stains a deep blue and the 

 greatest number of nuclei are found in the so-called resting 

 condition, indicating that the cells are quite active in their 

 metabolic process. 



Internal infection is accomplished by the fungus passing 

 from cell to cell, penetrating the cell wall, and as the myce- 

 lium is very thick, frequently 1.4 to 2/t at this stage, it 

 must secrete an enzyme which is capable of dissolving the 

 cell walls so as to allow three or more parallel strands of 

 hyphae to pass into a cell (f. 32). The fungus directs 

 itself toward the cell nucleus, in the neighborhood of which 

 it must derive its greatest benefit. Subsequent to this stage, 

 the mycelium grows very rapidly and begins to branch and 

 coil itself on one side of the nucleus, which is frequently 

 crowded to the wall; occasionally, however, instances are 

 found where the nucleus is contained within the fungal mass. 



Although this fungus is considered a parasite there are no 

 indications of such relationship as exist between the hausto- 

 rium of the mildews and the nucleus of their respective host 

 cells where it has been shown that the nucleus becomes very 

 irregular and surrounds closely the haustorium, in which 

 condition both nucleus and cytoplasm are ultimately ab- 

 sorbed by the fungus. Another singular feature is the fact 

 that there is no apparent hypertrophy of the host cell, such 

 as occurs so commonly among cells infected by the rusts. 

 Apparently the host cell of Myrica affords less resistance to 

 its fungus than the host cells of various plants offer to their 

 respective mildews and rusts; even the host cells of Ceanothus 

 and Elaeagnus display a greater resistive power. 



The host cell undergoes but few changes after the fungus 

 makes its entrance. First the starch grains, which are used 

 as food, disappear, the cytoplasm of the host cell, which at 

 first increases, gradually becomes less dense and finally van- 

 ishes (f. 33, 37). Comparative measurements were made 

 of the nuclei and cells of infected and neighboring unin- 

 fected regions, and it was found that there is no increase in 



