190 



AGRICULTURAL REPORT. 



Fiff. 27. 



class and color. The healthy bark did not exhibit any spores under the 

 same conditions. Fig. 27 represents the general appearance of the 

 cellular matter, spores of the blighted bark in their arrangement, 



form, and depth of color. I 

 treated blighted pear-tree 

 leaves in a similar manner. 

 On removing a portion of 

 their ei)idermis to glass mi- 

 croscopic slides, by means of 

 a knife, weU-defined ellipti- 

 cal double-celled spores were 

 seen, perfectly developed, 

 under a one-eighth power. 

 Fig. 28 represents the spores 

 on a portion of a leaf-rib, all 

 highly magnified. The cel- 

 lular structure of the leaf, 

 when viewed under a high 

 power, appeared as at 2. 

 About one-half of the cells 

 were filled with a dark-brown 

 opaque substance, the other 

 half being highly transparent 

 while 3 shows the appearance 

 of the leaf blackened from in- 

 ternal disorganizations, and 4 represents a single stratum of mycelium 

 which appeared on leaves that had been only partially submerged in water. 

 It had a very fine silken appearance. From its great delicacy it could not 

 be removed from its i)ositiou, without injury, by any of the ordinary 

 modes, as with a point ; and in case spores were i)resent their true po- 

 sitions could not be seen. To overcome this diflSculty 1 prepared a ^'ery 

 limpid solution of copal varnish, by combining one ounce of copal with 

 ten of benzine, a portion of which I poured on a glass slide one inch by 

 y- 28. three, instantly allowing all 



the superfluous varnish to 

 drain off. In about thirty 

 minutes after this operation 

 the mildewed leaf was 

 pressed gently on the var- 

 nished glass, when the my- 

 celium was transferred to it, 

 owing to the slightly' sticky 

 character of the varnish. 

 When mounted in the usual 

 manner they may be photo- 

 graphed. The threads of the 

 mycelium are not more than 

 about the twenty - thou- 

 sandth of an inch in diame- 

 ter ; from these short threads 

 protrude, on the terminals of 

 which grow bundles of naked 

 spores, arranged as shown. 

 In my investigations of 

 pear - tree blight, I have 

 failed to discover any fungi inhabiting those portions of blighted bark 

 which seem deficient of albuminous matter. 



