14 



lettuce we find that Botrytis has no connection whatever with the 

 real Drop, but that it is caused by the Sclerotinia. In such cases 

 the disease does not usually appear until just before the crop 

 matures. Its effect is very similar to that of the Botrytis in similar 

 plants. There is this difference, however, that the plant goes off 

 more suddenly and collapses more completely, showing that the fun- 

 gus is more active. Usually but a single night elapses from the 

 time when slight wilting is noticed until the whole plant, head and 

 all, lies flat on the ground. (See Fig. 4.) The stem and bases of 

 the leaves are found to be full of the fungous growth, (see Fig. 5.) 



which appears on the surface as a 

 delicate, white mould. The plant 

 usually rots more completely than 

 when attacked bv Botrvtis and soon 

 the mould spreads to the soil, mak- 

 ing a luxuriant growth upon the sur- 

 face and reaching out to attack neigh- 

 boring plants. If it reaches a leaf, 

 stem, or any part of a plant, it soon 

 spreads over and penetrates it, works 

 down into the stem and produces the 

 disease. This fungus produces no 

 spores as found in Botrytis. On 

 plants in the early stages of decay it 

 consists simply of a mass of fungous 

 threads which reproduce only by 

 direct growth on the plant or soil, being able to live and grow on 

 either. Later, however,- when the affected plant becomes dead and 

 dried up, there may be found on the under side- of the old remains 

 next the soil, very small black granules looking something like the 

 excrements of mice. These are called sckrotia. (See Fig. 6.) 



They are simply solid masses of 

 the substance of the fungus, 

 which are not so delicate as the 

 mould-like growth, and hence 

 are better able to withstand 

 heat, drying, etc. Sclerotia of 

 larger size are sometimes pro- 

 duced and from these a kind 

 of spore is developed, (See 

 Fig. 7.) but it is very doubt- 



FiG. 6. Mycelium and sclerotia of the f^j jf ^his ever OCCurS in the 

 Drop fungus. 



Fig. 5. Filaments of Sclerotinia in 

 lettuce stem. 



