227 



Fiff. 1. 



In entering upon an investigation of this kind, it is necessary, some- 

 times, to experiment with suspected wood fibers taken from living or 

 dead organic matters, with a view of developing to a higher state of 

 growth the dormant germs. Some of the means employed consist in 

 subjecting suspected specimens to a favorable temperature and moisture, 

 and suitable food ; in this way, sometimes, forms will be exhibited after 

 the lapse of a suitable period, by which means the true character of the 

 fungi is known. In examining pear-tree blight, I have taken advantage 

 of such means to ascertain the presence of fungi in suspected portions 

 of an affected pear-tree. I removed several portions of the bark from 

 yarious points of the tree, and examined them with an object-glass of 

 about one inch, which for this puri)ose may be. considered a low power, 

 but no well-defined forms of nitcelium (spawn) were visible. I next 

 placed specimens of the healthy bark and the blighted in separate 

 vessels of water, to be macerated; in about eight days the blighted 

 portions indicated the separajiion of the last cambium layer from tho 

 liber, which appeared as a translucent membrane, the largest portions 

 of which were not over one-tenth of an inch, and did not exceed one- 

 hundredth of an inch in thickness. When a portion of the flocculent 

 matter was placed under an object-glass of about 250 diameters, its 

 ©ellular structure was seen, 

 yrell defined, and numerous 

 dark-brown spores bounded 

 most of the cell walls. [See 

 Pig. 1.] In some cases the 

 cells exhibited nothing but 

 dar*k masses of brown gela- 

 tinous matter, but when 

 subjected to pressure and 

 friction they were found to 

 be masses of spores, all of i 

 the same class and color. 

 The healthy bark did not I 

 esLhibit any spores under the 

 same conditions. Fig. 1 

 represents the general ap- 

 pearance of the cellular mat- 

 ter, 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 ot their epidermis to glass microscopic slides, by 

 means of a knife, well-defined elliptical double-celled spores were seen, 

 perfectly developed, under a one-eighth power. Fig. ti represents the 

 spores on a portion of a leaf-rib, all highly magnified. The cellular 

 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 internal 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 position, without injury, by any of the ordinary modes, as witli 

 a point ; and in case spores were present their true positions could not 

 be seen. To overcome this difiiculty I prepared a very limpid solution 



