Ill 



The spore-clusters are quite distinct at first, but may run together 

 after a short time, and the entire surface appear to be covered with 

 an incrustation of spores if the air be dry, or with a somewhat 

 gelatinous covering if the air be moist. 



Fie. 124. Stromaof the Dematium-l&e fungus causing 



the blight of cherries shown in Fig. 123. It will be ^ o 



seen that the hyphee forming the stroma are for 



the most part without spores, this being due c 



to the process of sectioning and mounting. At 



a, however, fresh spores are starting; b, hypha 



with five spores that have remained attached ; c, 



tissue of the cherry that has become brown owing 



to the attack of the fungus ; d, surface of the 



cherry. A newer or younger stroina than that 



shown may be sectioned so that a much larger 



proportion of the spores will remain attached to 



the hyphae. Several of the escaped spores are 



shown above the stroma. X 200 



7-5 



19- 



20- 



10-6 



11-8 

 2'5 

 87 



10-4 

 8-3 

 6-5 



3-7 



5- 



3-3 



4-5 



2-8 



1-5 



25 



2-8 



3- 



2-7 



Av. 10 5 x 3-2 



As to the spores themselves, the measurements of ten spores, taken 

 at random, are given in the margin, and it will be seen 

 that the average is 10'5 x 3*2 /x., the range being 2'5-20 

 x l'5-5 /x. This range in the size of the spores is far 

 greater than is usual among fungus species. When 

 these spores are placed in water they have not, with me, 

 so far, shown a tendency to sprout and form a mycelium. 

 When placed in an infusion of cherries, however, I 

 have noted that they bud copiously after the manner 

 of yeast, and from this cause the number of spores 

 increases, while their size decreases. The spores, when 

 undergoing this process of budding, often show vacuoles, 

 while the original spores, as obtained from the surface of cherries, 

 were often without vacuoles and with very little internal differentiation. 



Sections across the areas where the snow-white cushion-shaped 

 spore masses have been pushed forth, show slightly-raised beds from 

 which the spores are produced. In the sections mounted in water 

 these beds are destitute of spores, except of the very smallest size, all 

 the others having been washed away. The hyphae upon which the 

 spores are borne are of a larger diameter than the spores themselves. 

 On some occasions it is possible to see these small spores growing on 

 the ends of the hyphae of the stroma, and it is then apparent that the 

 spores are borne in numbers on each hypha. In sections made from 

 fresh material, while the hyphae are 9-13 /x in diameter the spores are 

 1*5-5 /x in diameter. The spores are ellipsoidal or elongated in form, 

 being very seldom of exactly the same form at the two ends. The 

 broader hyphae on which they are borne are several times as long as 

 the spores themselves, and are unbranched and packed close together 

 in the stroma, which is only slightly raised above the surface of the 

 diseased area. All these appearances can be seen only with the aid 

 of medium or high powers of the microscope. The smallest stroma 

 seen was not more than four to five times as wide as the spore- 

 bearing hyphae that is to say, measured 40 /x. The larger spore 

 beds measure 180 /u, and upwards. (See Fig. 124.) 



The septate mycelium seen in the diseased cherries was colourless, 

 and varied in diameter from 3 to 9 micromillimetres, one of its 



