92 State Horticultural Society. 



In the presence of moisture the rigid wall of the spore breaks and 

 the protoplasmic contents grow out in the form of a delicate tube, which 

 is called the germ tube. The germ tube grows along the surface of the 

 leaf until it either finds an opening or makes one. In a great many cases 

 the germ tube enters the leaf through one of the natural pores in the 

 epidermis of the leaf. Once inside of the leaf, the germ tube becomes 

 thicker and grows deeper into the plant, absorbing its nourishment from 

 the living cells. 



This process of germination gives the horticulturist a splendid op- 

 portunity for killing the fungus with his spraying solutions. The spore 

 is a difficult thing to kill, and would require a mixture so strong as to 

 be injurious to the fruit tree; but the little germ tube is very delicate and 

 easily injured. Hence if the leaves of a tree are covered with Bordeaux 

 mixture, it need not be strong enough to kill the spores, but will kill the 

 germ tube and prevent its penetration into the leaf. This teaches also 

 that it is best to spray early and keep the leaves covered with the spraying 

 mixture until all danger is passed, because, when once inside the tree, 

 it is almost impossible to reach the fungus. 



HOW DOES A FUNGUS CAUSE INJURY? 



It has already been said that parasitic fungi rob the living cells of 

 their host plant of food. A very natural result follows, namely, the 

 death of the cells ; but before some of them die they are stimulated to 

 abnormal growth. An example of this is seen in the peach-leaf curl. 



A large number of fungi never grow very far into the host plant, 

 beyond the point of infection, and cause only local disease, frequently 

 with no perceptible disturbing eflfect upon the host. Such is the case, 

 particularly with leaf-spot diseases; the tissues of isolated spots are 

 killed and fall out, giving the leaf the so-called "shot-hole" effect. In 

 contrast to these there are fungi which, directly or indirectly, bring 

 about the death of their host, or some part of it. 



The death of the host may be caused by the poisonous action of sub- 

 stances excreted by the fungus, which happens in the case of potato blight ; 

 or they may grow so vigorously in the water-conducting channels as 

 to kill them and choke up the channels through which the water rises. 

 Certain cankers penetrate the delicate, growing portions of the tree and 

 destroy them, causing the death of those parts of the tree and all above 

 them. 



In the third place, there are many fungi which inhabit a plant with- 

 out disturbing the development of any part, or causing immediate death, 

 yet with such effect that the growing period of the organ in question is 



