MICROSCOPIC INVESTIGATION. 189 



under such conditions are comparatively empty, and have room for the 

 expansion of any limited portions of sap remaining. Climatic derange- 

 ment in the animal as well as in the vegetable economy is frequently 

 produced from sudden changes of temperature. A mantle of ice, or of 

 snow, will not necessarily prove hurtful to plant-life ; flowers are some- 

 times found blooming under snow. It is from the unprepared condition 

 of plants and trees that injury from frost mostly springs. It is not un- 

 usual for a shepherd on the mountains of Scotland, while tending his 

 sheep, to save them from perishing in snow-drifts, to immerse his plaid 

 in a brook, wring it out, and wrap it round himself. It freezes, and ice 

 being a non-conductor of heat, he is kept warm in his frozen mantle. 

 The Laplander lives in huts of ice or snow to shield himself and family 

 froui the bleak winds of winter. Ice, snow, and water are classed as 

 non-conductors. It is when water is converted into vapor that the 

 body from which it evaporates becomes cold. MiUions of pounds of 

 paraffine have been for a long period annually extracted from coal-oil by 

 taking advantage of this principle ; by the evaporation of ether in coii- 

 tact with a vessel containing coal-oil the parafiBLne freezes solid in the 

 oil and is thereby easily removed. But it is not the cold, properly con- 

 sidered, which produces the disease owing to the bursting of plant-cells, 

 but to the stoppage of the functions of assimilation in the presence of 

 myriads of germs of fungi and infusorial life. Healthy plants will de- 

 compose any foreign substance suitable for their food and assimilate it 

 in the support of their own function. 



" Fungi consist of two principal elements, the vegetative and the fruc- 

 tifying. If we take, for example, the common mushroom, the vegeta- 

 tive is represented by the spawn which, for a time, carries on all exist- 

 ing functions of the plant ; the fructifying by the stem, with the cap 

 and gills, which bear nearly the same relation to the spawn as the flower 

 with its various organs to the stem on which it grows. The spawn 

 may flourish for years without bearing any fruit, but fruit can nevec be 

 produced without spawn." 



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

 times, to experiment with suspected wood-tibers taken from hving 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 afi'ected pear-tree. I removed several portions of the bark from 

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

 about one inch, which, for this purpose, may be considered a low power, 

 but no mycelium was 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 separation of the 

 last cambium layer from the liber, which appeared as a translucent mem 

 brane, 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 cellular structure was seen, well defined, 

 and numerous dark-brown spores bounded most of the cell-walls. 

 [See Fig. 27.] In some cases the celle exhibited nothing but dark 

 masses of brown gelatinous matter, but when subjected to pres- 

 sure and friction they were found to be masses of spores, all of the same 



