258 ROMANCE OF LOW LIFE AMONGST PLANTS. 



maturity become subjected to the disease. In the 

 next stage we discover that this mycehum has de- 

 veloped erect branched threads, which pass out 

 through the stomata again into the external air, 

 sometimes singly, sometimes in tufts. These are 

 the fertile threads of the mould, which soon produce 

 a single conidium at the tip of each of the branchlets, 

 just like the original conidium whence the zoospores 

 were developed (Fig. 51). When fully matured each 

 fertile thread produces a score or more of these conidia, 

 which fall away when ripe, and then undergo trans- 

 formation into zoospores, ready and active, prepared 

 to pass through the same stages again, and indefi- 

 nitely multiply the pest. This history represents the 

 ordinary conidial fructification of the mould, by 

 means of which it is passed from leaf to leaf and 

 from plant to plant, until the whole area is affected. 

 How many of the minute conidia may be transported 

 to a considerable distance by a breath of wind it is 

 impossible to say, but it is known that they are 

 capable of suspension in the air, and that they may 

 be carried to any spot where there is sufficient 

 moisture for the conidia to be differentiated into 

 zoospores, and afterwards come to rest and germi- 

 nate. This process takes place in summer and 

 autumn, but there is yet another means by which 

 the pest is disseminated in the spring. 



The mycelium which flourishes within the sub- 

 stance of the plant infested is capable of producing 

 larger globose bodies, chiefly within the stems, con- 

 cealed from external view. These globose bodies 

 secrete a thick envelope, mostly of a brownish colour, 



