12 BOARD OF AGRICULTURE. 



Planta take their food directly fmm tlie eoil by myriads of mouths situated 

 in tiuir roors. It ia in a state of the Giicst poa^ilile divit-ion and solution, and 

 conscqiiently needs no tedious mastication and dijjestion. It jjoes l)y one set 

 of vessels through the brandies to the leaves, which constitute their lun}j;8. 

 Here it is exposed to the action of the air, its color is changed, oxygen and 

 ■water are emitted by dav, and a small quantify of carbonic acid gas by night, 

 •tie purified sap or lymph returns by another set ol vessels situated along the 

 bark, ministering to the support and growth of the whole plant, each leaf, 

 flower, fruit, seed and structure, selecting with unerring instinct, what is 

 adapted to its peculiar organization. Thus the two sustain a mutual relation 

 to each other. Plants emit oxygen which is essential to the existence of ani- 

 mala, while carbonic acid gas is nearly as important to healthy vegetation. 



Vegetables have the principle of vitality which works in a mysterious man- 

 ner fieculiiir to itself. Alone it eludes our knowledge, but when acting on 

 matt(!r and blended with it, we see its wonderful influence and power. From 

 the simple acorn or seed it builds up the sturdy oak and graci'ful elm. It 

 holds in abeyance all the laws of chemical decomposition. It m;iy lonir delay 

 the onward march of death, but when it ceases to act, all organic matter is 

 resolved into its constituent parts. Then the very air and heat, that once 

 ■were the sources of vigor and growth of planta, become the swift agents of 

 their destruction. They return to dust from which they originated. 



It should then be our endeavor to ascertain the conditions on which vitality 

 depends and the various causes which impair it, that we may promote the 

 one, and remove the other, and thus we may both prevent and cure the dis- 

 eases of vegetat'on. 



A correct knowledge of these conditions forms the basis of all systematic 

 vegf^tablo pathology. We proceed to enumerate some of the most important. 

 All vegetables with scarcely an exception, contain a considerable quantity of 

 mineral ingredients which, dissolved by water, they absorb by their roots. 



By interrogating analytical chemistry, we learn the quantity and kinds of 

 mineral matter the diffTent plants require, and also wtiat missing or insuffi- 

 cient ingredients to supply to the soil to enable us to raise any desired crop. 

 Thus an avera-je crop of wheat grown on an acre of ground needs only 30 

 pounds of potash, while turnips on the same surface must be furnislied with 

 230 pounds, and potatoes still more. This i-f but one instance of a single 

 element required. If then, any particular plant has not supplied to its roots 

 enough of the minora! substances it needs, or if water enough is not furnished 

 to dissolve its solid food and to form a part of its own composition, it sickens 

 and dies. 



Besides, plants require carbon and other inorganic elements which once 

 constituted living vegetable structure that has decayed and been converted 

 into mould or loam, to yield suitable food for another generation. They also 

 need nitrogen, which as it respects our cultivated crops must have formed 

 part of an animal organization. They must receive it in the form of ammonia. 

 If an insuiBcient quantity of these elements is not supplied, disease and decay 

 result. 



Ail the different elements that compose the food must gradually be added to 

 the sip that is constantly contributing to the structure of the plant which has 

 the ability to manufacture, from the circulating fluid, those albuminous, 

 starchy and oily coippounds adapted to its wants. If this power of assimila- 

 tion, or changing them to its own substance by digestion is impaired, disease 

 and death are induced. 



The sap must fli)w in constant round from roots to leaves, there absorb car- 

 bonic acid gas, evolve oxygen, and then proceed onward to nourish all parts 

 of the plant. If these functions of circulation and respiration be much 

 impaireH, fatal consequenecs must result. 



Ilf'jit is anotiier condition of the vitality of plants, varying in amount in 

 diff-rent kinds. Wheat cannot mature at a lower temperature than 'IT) deg., 

 potatoes at not less than 52 deg., barley at not less than 59 deg., and Indian 



