— 174 — 



cells in place of disorganized chlorophyll and protoplasm, — a sure 

 sign of lowered vitality, — and gives the reddish appearance seen 

 from without. The mycelium continues to ramify from the cen- 

 ter of the spot, where it has begun its work, attacking and de- 

 stroj'ing other cells, all those within reach of the denser growth of 

 filaments, shrivelling, drying, and finally filling with air. It is 

 this last change which gives the dead- white appearance to the 

 center of the spot. It will be seen from the figures that the white 

 area is only about one-fifth the thickness of the health}^ portion of 

 the old leaf, and of course its cells have completely lost their vital- 

 ity. If these centers of the disease are numerous and coalesce, it 

 will be seen that the whole leaf must succumb and die, an event 

 of frequent occurrence in seasons favoring the fungus. If a .sec- 

 ond crop of leaves is put out in August, these may in turn be in- 

 fected from the diseased ones, and either much injured or destroyed, 

 in which case the plants should be plowed up, as no crop can be 

 expected from them the following year. 



Especial attention was directed to the hibernation of the ordi- 

 nary mycelium. Leaves were brought in repeatedly during 

 periods when they were not covered with snow, and placed in a 

 warm, moist chamber. It was found that basidia invariabl}^ de- 

 veloped from the borders of the white spots in less tlian twenty- 

 four hours and produced conidia exactly like the sunniier conidia. 

 This demonstrated the presence of active mycelium about the 

 disease centers. In the early spring it was found that wholly 

 new spots would appear on diseased leaves, in so short a time 

 after they were brought into the laboratory that no infection 



Fig. 3.— Cross section 

 of the upper epidermis 

 of a leaf showing the 

 basidia (b) and conidia 

 (c) of Sphaerella Fra- 

 gariae. 



Fig. 4. — The conicUa enlarged from 

 Fig. 3- 



