that when it does come up against you you will not be 

 worsted in the contest. 



Life History of the Scab Fungus. The apple scab, as 

 every man in this room must know, is a disease caused by a 

 fungus, a minute plant living upon the leaf, fruit, and rarely 

 the twigs of the apple. It is a parasite, at least during the 

 growing season of the apple tree. Before entering into a 

 discussion of the control of this scab fungus we shall do well 

 to have before us the chief facts of its life and existence 

 during the round of the seasons. The fungus pa-sses the win- 

 ter in the old leaves on the ground. When the scabby leaves 

 fall from the apple tree in autumn the fungus which has 

 been living on the surface now grows into the tissues of the 

 dead leaf and there forms large numbers of globose spore 

 cases, more minute than the head of a pin. These grow dur- 

 ing the autumn and mature in the early spring, appearing 

 as very small black pimples discernable by the aid of a hand 

 lens, just under the skin of the leaf on the side lying upper- 

 most. The spores in these pimple-like cases are produced 

 eight in a sack called an ascus. Fifty or more of these asei 

 are produced in each spore case. These spores are ripe at 

 about the time the blossom clusters begin to show a trace of 

 pink and during the rains which usually come at this period 

 are forcibly discharged into the air. Within five minutes 

 after the old leaves on the ground are wetted spores begin 

 to be discharged. Mr. Wallace, working in our laboratory 

 some years ago showed that no less than 8,107,200,000 spores 

 may readily be discharged in 45 minutes of rainy weather, 

 from the leaves on the ground under a tree having a spread 

 of 40 feet. These spores while shot less than a quarter of 

 an inch into the air are very light and float off on the slight 

 air currents to lodge on unfolding leaf, flower bud, or pedi- 

 cle. If the rainy weather which has brought about the dis- 

 charge of these ascospores continues for 30 to 40 hours so 

 that the foliage and blossom clusters remain wet the spores 

 germinate and sending a germ tube into the skin of the leaf 

 establish the parasite which within 10 to 14 days develops 



