THE ART OF CULTURE. 



tmctly heard at the distance of several feet. 

 Here the carbonic acid rising to the surface 

 displaces completely all the air, and conse- 

 quently all the oxygen, from the soil; and 

 and without oxygen neither seeds nor roots 

 can be developed; a plant will not vegetate 

 in pure nitrogen or carbonic acid gas. 



Humus supplies young plants with nou- 

 rishment by the roots, until their leaves are 

 matured sufficiently to act as exterior organs 

 of nutrition; its quantity heightens the fer- 

 tility of a soil by yielding more nourishment 

 in this first pe'riod of growth, and conse- 

 quently by increasing the number of organs 

 of atmospheric nutrition. Those plants 

 which receive their first food from the sub- 

 stance of their seeds, such as bulbous plants, 

 could completely dispense with humus ; its 

 presence is useful only in so far as it in- 

 creases and accelerates their developement, 

 but it is not necessary indeed, an excess of 

 it at the commencement of their growth is 

 in a certain measure injurious. 



The amount of food which young plants 

 can take from the atmosphere in the form of 

 carbonic acid and ammonia is limited ; they 

 cannot assimilate more than the air contains. 

 Now, if the quantity of their stems, leaves, 

 and branches has been increased by the ex- 

 cess of food yielded by the soil at the com- 

 mencement of their developement, they will 

 require for the completion of their growth, 

 and for the formation of their blossoms and 

 fruits, more nourishment from the air than 

 it can afford, and consequently they will 

 not reach maturity. In many cases the 

 nourishment afforded by the air under these 

 circumstances suffices only to complete the 

 formation of the leaves, stems, and branches. 

 The same result then ensues as when orna- 

 mental plants are transplanted from the pots 

 in which they have grown to larger ones, 

 in which their roots are permitted to increase 

 and multiply. All their nourishment is em- 

 ployed for the increase of their roots ami 

 leaves; they spring, as it is said, into an 

 herb or weed, but do not blossom. When, 

 on the contrary, we take away part of the 

 branches, and of course their leaves with 

 them, from dwarf trees, since we thus pre- 

 vent the developement of new branches, an 

 excess of nutriment is artificially procured 

 for the trees, and is employed by them in 

 the increase of the blossoms and enlargement 

 of the fruit. It is to effect this purpose that 

 vines are pruned. 



A new and peculiar process of vegetation 

 ensues in all perennial plants, such as 

 shrubs, fruit and forest trees, after the com- 

 plete maturity of their fruit. The stem of 

 annual plants at this period of their growth 

 becomes woody, and their leaves change in 

 colour. The leaves of trees and shrubs, on 

 the contrary, remain in activity until the com- 

 mencement of the winter. The formation 

 of the layers of wood progresses, the wood 

 becomes harder and more solid, but after 

 August the leaves form no more wood; all 



the carbonic acid which the plants now ab- 

 sorb is employed for the production of nu- 

 tritive matter for the following year : instead 

 of woody fibre, starch is formed, and is dif- 

 fused through every part of the plant by the 

 autumnal sap (seve d'Aout.)* According 

 to the observations of M. Heyer, the starch 

 thus deposited in the body of the tree can be 

 recognised in its known form by the aid of a 

 good microscope. The barks of several as- 

 pens and pine-treesf contain so much of this 

 substance, that it can be extracted from them 

 as from potatoes by trituration with water. It 

 exists also in the roots and other parts of pe- 

 rennial plants. A very early winter, or sudden 

 change of temperature, prevents the forma- 

 tion of this provision for the following year; 

 the wood, as in the case of the vine-slock, 

 does not ripen, and its growth is in the next 

 year very limited. 



From the starch thus accumulated, sugar 

 and gum are produced in the succeeding 

 spring, while from the gum those constitu- 

 ents of the leaves and young sprouts which 

 contain no nitrogen are in their turn formed. 

 After potatoes have germinated, the quantity 

 of starch in them is found diminished. The 

 juice of the maple-tree ceases to be sweet 

 from the loss of its sugar when its buds, 

 blossoms, and leaves attain their maturity. 



The branch of a willow, which contains 

 a large quantity of granules of starch in 

 every part of its woody substance, puts forth 

 both roots and leaves in pure distilled rain- 

 water; but in proportion as it grows, the 

 starch disappears, it being evidently ex- 

 hausted for the formation of the roots and 

 leaves. In the course of these experiments, 

 M. Heyer made the interesting observation, 

 that such branches when placed in snow 

 water (which contains ammonia) produced 

 roots three or four times longer than those 

 which they formed in pure distilled water, 

 and that this pure water remained clear, 

 while the rain-water gradually acquired a 

 yellow colour. 



Upon the blossoming of the sugar-cane, 

 likewise, part of the sugar disappears ; and 

 it has been ascertained, that the sugar does 

 not accumulate in the beet-root until after 

 the leaves are completely formed. 



Much attention has recently been drawn 

 to the fact that the produce of potatoes may 

 be much increased by plucking off the blos- 

 soms from the plants producing them, a 

 result quite consistent with theory This 

 important observation has been completely 

 confirmed by M. Zeller, the director of the 

 Agricultural Society at Darmstadt. In the 

 year 1839, two fields of the same size, lying 

 side by side and manured in the same man- 

 ner, were planted with potatoes. When the 

 plants had flowered, the blossoms were re- 



* Hartig, in Erdmann und Schweigger-Seidels 

 Journal, V. 217. 1335. 



T It is well known that bread is made from the 

 bark of pines in Sweden during famines. 



