2;3 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



also characteristic of these hyphae 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 PhytopJithora omnivora. 



The hyphae which project from the epidermis intc 

 the damp air proceed to develop certain spon 

 known as the conidia, which are capable of at on< 

 germinating and spreading the disease. These coni- 

 dia are essentially nothing but the swollen ends 

 branches of these free hyphae : the ends swell up an< 

 large quantities of protoplasm pass into them, an< 

 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 are, not 

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

 that (l) many thousands of these spores T may be forme 

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

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

 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 



1 I here use the popular term for them : they are more properly 

 called Conidia. 



