xiii.] "DAMPING OFF" OF SEEDLING-TREES. 279 



that this explains how it is that the disease is spread 

 in patches from centres, and also why the spread is so 

 rapid in close, damp weather. 



When a conidium germinates in a drop of dew for 

 instance, the normal process is as follows. The proto- 

 plasm in the interior of the pear-shaped conidium 



FIG. 44. Portion of epidermis of a beech-seedling, on which the conidia of the 

 Phytophthora. have fallen and butst, a and d, emitting the motile zoospores, b, 

 which soon come to rest and germinate, c, by putting forth a minute germinal 

 hypha, c, e, which penetrates between the cells of the epidermis, e andy, and 

 forms the mycelium in the tissues beneath. At d a zoospore has germinated, 

 without escaping from the conidium. (Highly magnified : partly after De Bary 

 and Hartig.) 



becomes divided up into about twenty or thirty little 

 rounded naked masses, each of which is capable of 

 very rapid swimming movements ; then the apex of 



