188 AGRICULTURAL REPORT. 



MICROSCOPIC INVESTIGATION. 



By Thomas Taylor, Micro'scopist. 

 PEAE-TEEE BLIGHT. 



" For nearly n liundred years blight of the pear has been a. terror and 

 despair to growers of its frnit.'' This disease is known under a variety 

 of names — winter or frozen sap blight, leaf blight, summer blight, &c. 

 It is quite different from insect blight. Since the temperature and 

 hygrometric state of the atmosphere and the conditions of the soil, 

 whether acid or alkaline, pulverous or stiff", affect fungi by either re- 

 tarding or fostering their growth, it becomes a matter of interest to 

 ascertain how far observations made in relation to i)ear-tree blight will 

 agree with the fungus theory. 



Some forms of fungus are favored by heat and dryness, such as the 

 oidium of the European gTape-vine, while the fungus of the native grape- 

 vine is favored in growth by moisture and heat. The first may be a 

 saccharine and the second an acid fungus, being favored by the con- 

 dition of the leaf and wood. 



Yeast, which is a fungus of a low order, when in its active state 

 always exhibits an acid reaction ; if well washed, the globules become 

 much less active ; but by exposure for a few hours to the air their activ- 

 ity is restored, the acidity being thereby again developed. The addi- 

 tion of a small quantity of vegetable acids, such as acetic or tartaric, 

 to washed yeast, immediately restores its activity, but when a larger 

 quantity of acid is employed the process of spore-budding is arrested. 

 The mineral acids, such as sulphuric, even in small quantities, immedi- 

 ately stop yeast fermentation ; sulphurous acid acts in like manner. 

 A small quantity of free alkali, or a strong solution of common salt, also 

 prevents its fermentation. ISfitrate of silver, corrosive sublimate, and 

 sulphate or acetate of copper, check its growth immediately on appli- 

 cation ; also oxide of manganese, oxide of mercury, strychnia, small 

 quantities of kreosote, oil of turpentine, and many other essential oils. 

 When, however, the low forms of fungi once commence, the vegetable 

 bases have no power of arresting although they may retard their iDro- 

 gress. Boiling water, also, for a time arrests the progress of fungi. A 

 knowledge of the habits of fungi and of the substances and conditions 

 which retard or foster their growth wUl, to some extent, enable fruit- 

 growers to modify fungus blight. But independent of all chemical ap- 

 pliances, drainage, and sheltering by belts of timber or hedges, would 

 he of great imi^ortance, when the land or orchard is devoid of natural 

 soul-ces of protection. It is not simply to the conditions of high or low 

 temperatures, or to the hygrometric state of the weather, that blight, 

 rust, molds, &c., owe their origin, but to a combination of many condi- 

 tions. Heavy rains on well-drained soil will not present the same con- 

 ditions to vegetable growth which they would on poorly-drained. A 

 favorable condition of soil and climate is required by foliage of spring, 

 summer, and autumn, for a healthy performance of its functions. Under 

 highly favorable conditions of cUmate and soil the wood becomes ma- 

 tured, and, consequently, the fruit and the leaves drop when, and only 

 when, the uses for which they were formed have been accomplished. 

 The wood of every tree when fully matured has condensed the sap, 

 forming it into wood or other solid material 5 consequently the cells 



