27S TIMBER AND SOME OF ITS DISEASES [chap. 



also characteristic of these hyphcB that they make 

 their way in the substance of the cell-walls, in what 

 is known as the " middle lamella " : in this, and in 

 what follows, they present many points of resem- 

 blance to the potato-disease fungus, which is closely 

 allied to Phytophtho7'a ommvora. 



The hyphse which project from the epidermis into 

 the damp air proceed to develop certain spores, 

 known as the conidia^ which are capable of at once 

 germinating and spreading the disease. These coni- 

 dia are essentially nothing but the swollen ends of 

 branches of these free hyphae : the ends swell up and 

 large quantities of protoplasm pass into them, and 

 when they have attained a certain size, the pear- 

 shaped bodies fall off, or are blown or knocked off. 



Now the points to be emphasized here arc, not so 

 much the details of the spore-formation, as the facts 

 that (l) many thousands of these spores^ may be formed 

 in the course of a day or two in warm, damp weather ; 

 and (2) any spore which is carried by wind, rain, or a 

 passing object to a healthy seedling may infect it (in 

 the way to be described) within a few hours, because 

 the spore is capable of beginning to germinate at once 

 in a drop of rain or dew. A little reflection will show 



■^ I here use the popular term for them they aie moie properly 

 called Comdza. 



