XIIL] "DAMPING OFF" OF SEEDLING-TREES. 283 



seed-bed, gathering strength, as it were, hour by 

 hour. 



But, although we have explained the rapid infection 

 from plant to plant, it still remains to see how it is 

 that if we sow the seeds in this bed next year, the 

 seedlings are almost certain to be generally and badly 

 attacked with the disease at a very early stage. 



When the fungus-mycelium in the cotyledons and 

 other parts of the diseased seedlings has become fully 

 developed, and has given off thousands of the conidia 

 above described, many of the branches in the dying 

 tissues commence to form another kind of spore 

 altogether, and known as an oospore, or egg-like 

 spore. This spore differs from the conidium in size, 

 shape, and position, as well as in its mode of develop- 

 ment and further behaviour, and if it were not that 

 several observers have seen its formation on the same 

 hyphae as those which give rise to the conidia, it might 

 be doubted by a beginner whether it really belongs to 

 our fungus at all. As it is absolutely certain, however, 

 that the oospore on germination gives rise to the 

 fungus we are considering, the reader may rest 

 satisfied on that point. 



The spore in question is formed in a swelling of the 

 free end of a branch of the hypha as follows (Fig. 45). 

 The protoplasm in the rounded end of the hypha 



