THE ART OF CULTURE. 



a certain height in the stem of the plant, 

 above which point it remains stationary. 



Just as germinating barley produces a 

 substance which, in contact with starch, 

 causes it to lose its insolubility and to be- 

 come sugar, so in the roots of the maple, at 

 the commencement of vegetation, a sub- 

 stance must be formed, which, being dis- 

 solved in water, permeates the wood of the 

 trunk, and converts into sugar the starch, or 

 whatever it may be, which it finds deposited 

 there. It is certain, that when a hole is 

 bored into the trunk of a maple-tree just 

 above its roots, filled with sugar, and then 

 closed again, the sugar is dissolved by the 

 ascending sap. It is further possible that 

 this sugar may be disposed of in the same 

 manner as that formed in the trunks; at all 

 events it is certain, that the introduction of 

 it does not prevent the action of the juice 

 upon the starch, and since the quantity of 

 the sugar present is now greater than can 

 be exhausted by the leaves and buds, it is 

 excreted from the surface of the leaves or 

 bark. (Certain diseases of trees, for example 

 that called honey-dew, evidently depend on 

 the want of the due proportion between the 

 quantity of the azotised and that of the un- 

 azotised substances which are applied to 

 them as nutriment. 



In whatever form, therefore, we supply 

 plants with those substances which are the 

 products of their own action, in no instance 

 do they appear to have any effect upon their 

 growth, or to replace what they have lost. 

 Sugar, gum, and starch, are not food for 

 plants, and the same must be said of humic 

 acid, which is so closely allied to them in 

 composition. 



If now we direct our attention to the par- 

 ticular organs of a plant, we find every fibre 

 and every particle of wood surrounded by a 

 juice containing an azotised matter; while 

 the starch, granules, and sugar are enclosed 

 in cells formed of a substance containing ni- 

 trogen. Indeed every where, in all the juices 

 of the fruits and blossoms, we find a sub- 

 stance destitute of nitrogen, accompanied 

 by one which contains that element. 



The wood of the stem cannot be formed, 

 quasi wood, in the leaves, but another sub- 

 stance must be produced which is capable 

 of being transformed into wood. This sub- 

 stance must be in a state of solution, and 

 accompanied by a compound containing ni- 

 trogen; it is very probable that the wood 

 and the vegetable gluten, the starch granules 

 and the cells containing them, are formed 

 simultaneously, and in this case a certain 

 fixed proportion between them would be a 

 condition necessary for their production. 



According to this view, the assimilation 

 of the substances generated in the leaves 

 will (cceteris paribus) depend on the quan- 

 tity of nitrogen contained in the food. When 

 a sufficient quantity of nitrogen is not pre- 

 sent to aid in the assimilation of the sub- 

 stances which do not contain it, these sub- 

 itances will be separated as excrements from 



the bark, roots, leaves, and branches. The 

 exudations of mannite, gum, and sugar, in 

 strong and healthy plants cannot be ascribed 

 to any other cause.* 



Analogous phenomena are presented by 

 the process of digestion in the human or- 

 ganism. In order that the loss which every 

 part of the body sustains by the processes 

 of respiration and perspiration may be re- 

 stored to it, the organs of digestion require 

 to be supplied with food, consisting of sub- 

 stances containing nitrogen, and of others 

 destitute of it, in definite proportions. If 

 the substances which do not contain nitrogen 

 preponderate, either they will be expended 

 in the formation of fat, or they will pass 

 unchanged through the organism. This is 

 particularly observed in those people who 

 live almost exclusively upon potatoes ; their 

 excrements contain a large quantity of un- 

 changed granules of starch, of which no 

 trace can be detected when gluten or flesh 

 is taken in proper proportions, because in 

 this case the starch has been rendered capa- 

 ble of assimilation. Potatoes, which when 

 mixed with hay alone are scarcely capable 

 of supporting the strength of a horse, form 

 with bread and oats a strong and wholesome 

 fodder. 



It will be evident from the preceding con- 

 siderations, that the products generated by 

 a plant may vary exceedingly, according to 

 the substances given it as food. A super- 

 abundance of carbon in the state of carbonic 

 acid conveyed through the roots of plants, 

 without being accompanied by nitrogen, 

 cannot be converted either into gluten, al- 

 bumen, wood, or any other component part 

 of an organ ; but either it will be separated 

 in the form of excrements, such as sugar, 

 starch, oil, wax, resin, mannite, or gum, or 

 these substances will be deposited in greater 

 or less quantity in the wide cells and vessels. 



The quantity of gluten, vegetable albu- 

 men, and mucilage, will augment when 

 plants are supplied with an excess of food 

 containing nitrogen ; and amrnoniacal salts 

 will remain in the sap, when, for example, 

 in the culture of the beet, we manure the 

 soil with a highly nitrogenous substance, or 

 when we suppress the functions of the leaves 

 by removing them from the plant. 



We know that the ananas is scarcely 

 eatable in its wild state, and that it shoots 

 forth a great quantity of leaves when treated 

 with rich animal manure, without the fruit 

 on that account acquiring a large amount 

 of sugar; that the quantity of starch in po- 

 tatoes increases when the soil contains much 

 humus, but decreases when the soil is ma- 



* M. Trapp, in Giessen, possesses a Cleroden- 

 dronfragrans, which grows in the house, and ex- 

 udes on the surface of its leaves in September 

 large colourless drops of sugar-candy, which form 

 regular crystals upon drying ; I am not aware 

 whether the juice of this plant contains sugar. 

 Professor Redtenbacher, of Prague, informs me 

 that he has analysed the crystals, and found them 

 to be perfectly pure sugar. ED. 



