supplement. SCIENCE AND ART OF AGRICULTURE. 1297 



proportion ; and if we do this by manure, of course it follows that there is a certain fixed proportion be- 

 tween the manure and the crop. Calculation will show us that although at first sight the gross weight 

 of the crops of a rotation is considerably above that of the manure applied, still, in reality, the amount 

 of the various elementary matters is much nearer an equality, in fart, are generally most abundant in the 

 manure. Let us, for example, suppose the following case : — an imperial acre of turnip soil receives 

 25 tons of farm-yard dung, and yields, 1st, 30 tons of turnips ; 2d, 42 bushels (of 53 lbs. each) of barley, 

 with 2000 lbs. of straw; 3d, 200 stone of hay ; 4th, 48 bushels (of 42 lbs. each) of oats, with 2500 lbs. of straw! 

 Now, the gross weight of these crops would be 80,342 lbs. whereas the manure would weigh only 56,000 lbs.; 

 and consequently, the soil has yielded 24,342 lbs. more in four years than it received in the form of ma- 

 nure, or at the rate of 6085J lbs. more annually. If, however, we compare separately the relative quan- 

 tities of carbon, azote, and saline matter contained in the crops and manure, we shall obtain the following 

 results : 



9,622-89 19,1184 



So that, in fact, there is a considerable excess in the manure, of all the elementary ingredients of the 

 crops, if we except the elements of water, viz., oxygen and hydrogen. ^Ye trust that this caculation will 

 he sufficient to satisfy all, that there exists a certain proportion between the weight cf the elements of 

 the crop and that of the constituents of the manure." 



8094. A rotation of crops is required, not merely because it tends greatly to lessen the expense of culti- 

 vation, but because the more azote a plant contains, the less frequently can it be cultivated upon the same 

 spot in uninterrupted succession. " The precise chemical principles upon which a rotation depends are 

 somewhat obscure." 



8095. A naked summer fallow only becomes necessary when soil cannot be cleaned and brought to a 

 sufficiently fine tilth between harvest and the following seed time, without interfering with other operations. 



80S6 — IV. The Economy of Husbandry, or the particulars regarding each individual crop, which 

 are necessary to be known in order to its successful cultivation. The following general facts in vegetable 

 physiology will assist us in understanding this part of the subject. 



8097. — 1 . All plants in a highly artificial state require a larger svppli/ of nourishment during the first 

 period of their growth than is supplied by the seed alone ; and hence the necessity of a rich soil, or of a 

 supply of putrescent manure. 



8098 2. Plants which have more than one method of propagating themselves should be limited to the 



method which is most suitable. The potato should not be allowed to produce seed, because it is most con- 

 veniently propagated by the tuber. 



8099.-13. Plants lay up a store of nourishment for the next year, either in the wood or roots, as in trees 

 and perennials, or in the seeds as in animals. 



8100 4. The starch of plants is altrays contained in cells, formed of a substance containing azote; 



and " consequently there exists a fixed proportion between the quantity of azote composing the cells 

 and the amount of starch contained in them ; hence it follows, that to increase the quantity of starch in 

 a plant, you must increase its supply of azote, although starch itself contains no trace of this element." 



8101. — 5. In all parts of a plant there is an exact proportion between the various elements entering into 

 its composition, so that an addition to one of them is necessarily followed by a relative addition to them all. 

 " If, for example, a plant possesses one part containing 2 grs. of azote, combined with 18 grs. of other 

 elements, and another portion containing 2 grs. of azote combined with 48 grs. of other elements , if we, 

 by any means, prevent the development of the more highly azotised portion, viz., the 2 to 18, we shall 

 produce a proportional increase in the other ; so that, by preventing the formation of 20 grs. of the highly 

 azotised portion, we obtain 50 grs. of that which contains proportionally less azote." 



" These facts will assist us in the following explanations regarding individual crops." 



8102. The turnip. " The fusiform, or globular part of the root of the turnip, contains the supply of 

 nourishment required for the development of the flower and seed in the following year. The turnip has 

 a large system of leaves ; contains much water ; is not highly azotised ; the seed possesses a very small 

 supply of nourishment ; the whole success of the crop depends, within certain bounds, upon the rapid 

 development of the large absorbent leafy surface. Hence the culture of the turnip must be conducted as 

 follows : — the soil must be sandy ; first, because it is a law that plants make preparations for retaining 

 in their own texture most water when the soil around them is capable of retaining least ; second, because 

 its development must be rapid, and hence the decomposition of manure must be rapid likewise. There 

 must be a good supply of very active manure, so that the seed may be provided with abundance of food 

 in the first period of its growth, and thus have its leaves developed as rapidly as possible (within 

 certain limits of course). As the plant is not highly azotised. it can draw the greater portion of its nou- 

 rishment from the air, provided the absorbent surface of the leaves be sufficiently large; hence it is more 

 necessary to attend to the quality than the quantity of the manure for this crop. A small quantity in a 

 very active state, will prove much more valuable here than a large quantity which is too fresh. As the 

 size of the bulb is regulated by the size of the surface of its leaves, this crop must not be too crowded, 

 but plentv cf room should be left to permit of the full development of the leaves." 



8103. the. potato. " The potato differs essentially from the turnip, in that the portion used is a per- 

 fectly developed part, that is to say, a part which is perfect in itself; for instance, the bulb of the turnip 

 is merely a deposit of nourishment for the use of the plant during the ensuing spring, and if removed 

 from the soil, cannot be made to produce a new individual ; w hereas the tuber of the potato is as much a 

 perfect individual as any seed, for it contains within itself all that is requisite for the propagation of the 

 species. On this account, therefore, the potato may be considered as perfectly developed w hen the tuber 

 is ripe ; whereas the turnip has merely advanced a "certain way towards perfection, which cannot be said 

 to occur until the seed is formed. Now, the importance of this distinction will be seen, when we re- 

 member that all plants deteriorate the soil most during the latter periods of their growth, and hence it 

 follows that, ceteris paribus, the potato is a more exhausting crop than the turnip. The potato, like 

 the turnip, has a large system of leaves, and contains much water. It is more azotised than the turnip, 

 but the portion containing the greatest quantity of azote is not developed until during the later periods 

 of the growth of the plant. It possesses two ways of propagating its species, viz., by seeds and tubers, 

 and whatever prevents the development of the one, increases proportionally that of the other ; this pro- 

 portion being regulated bv the auantity of azote. The success of the potato depends greatly upon a due 

 balance between the quantity of nutriment afforded respectively by the soil and the air, because the tuber 

 consists of a large deposition of starch in cells, composed of an azotised matter. Now, as the soil provides 

 the material for the cells, and the carbonic acid of the starch is derived chiefly from the air, it follows, 

 that if one or other of these supplies be in excess, a due proportion will not exist between the two in- 

 gredients of the tuber. Thus, if the soil be very rich in azotised matter, so many cells are produced that 

 the leaves cannot eliminate starch sufficient to fill them : on which account, the potato is of that peculiar 

 consistence termed ' waxv.' If, again, the soil is deficient in azote, only a few cells are formed, and these 

 are completely filled with starch, and the potato consequently becomes ' mealy.' With regard to the 

 order of development of these parts, the cells are first produced, and become filled with starch subse- 

 quently, and as this is formed by the leaves, any thing which injures them, such as frost, Ac, checks the 



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