1867. 



NEW ENGLAND FARMER. 



409 



that mineral, unless the soil be calcareous, 

 tends greatly to promote its growth and value, 

 both as regards the plant and seed. 



Prof. Johnston says, "a green crop plowed 

 in is believed by some practical men, to en- 

 rich the soil as much as the droppings of cattle 

 from a quantity of green food three times as 

 great." 



For the Kew England Farmer. 

 HOMT PLANTS GROW.— NO. III. 



By means of food derived from the atmos- 

 pliere and the soil. This food consists chiefly 

 of carbon, hydrogen and oxygen. Water con- 

 sists of oxygen and hydrogen, so that we may 

 say that carbon and water constitute the staple 

 food of plants. Nitrogen is found in some 

 plants, and phosphorus in the seeds of many. 

 These two latter elements do not seem essen- 

 tial to the growth of plants, for many are found 

 without them. 



Various salts, as lime, potash, soda, iron 

 and sulphur are held in solution in water, and 

 are drank in along with it by the radicles of 

 plants, and are deposited in the cells and in 

 their interstices, which compose the frame 

 work of plants, and contribute something to 

 their bulk, and serve to modify their pro- 

 perties and products. A large quantity of 

 water is drawn from the soil and strained 

 through the vessels of plants. A sunflower, 

 presenting between five and si.x thousand inches 

 of surface, was found by Hales to exhale from 

 twenty to thirty ounces of water daily, depend- 

 ing upon the condition of the atmosphere. 

 When this was in a condition to hold in solu- 

 tion the minute particles of water presented to 

 it upon the surfaces of the plant, the exhala- 

 tion went on vigorously. No perceptible ex- 

 halation occurred in dewy nights, because the 

 air then contained more water than it could 

 hold m solution. What quantities of water, 

 then, must pass through the immense surface 

 presented by the leaves of a large tree ! 



But this water leaves in the plant whatever 

 solid substances it contained in solution. In 

 many plants these earthy salts seem to serve 

 very little other purpose than to harden and 

 solidify the tissues. In others they combine 

 with acids that are formed in the vessels, and 

 serve to give character to the- plants, and are 

 Vound in their juices as oxalate of lime, malate 

 of lime, tartrate of potash, &c. Such salts 

 ire tbund most abundant in the leaves and 

 juits of plants ; in less quantity in the stems 

 ind roots. We have said the principal arti- 

 cles of plant footl are carbon, oxygen and hy- 

 drogen. Of these, carbon is the one most 

 abundantly worked up in the growth of the 

 plant. It is the material of which the root 

 and stem, the branches and leaves are chietly 

 composed. It is received into the plant in the 

 form of carbonic acid gas, or carbon combined 

 with oxygen, which naturally has a gaseous 



form. When received, united with water, 

 through the roots of plants, it is carried up 

 through the stems into the leaves. When re- 

 ceived through the pores of the leaves from 

 the atmosphere, it is immediately mingled with 

 the sap in the leaves brought up from the roots. 

 It is subjected to the action of the light in the 

 leaves, by which the oxygen is separated from 

 the carbon. The oxygen goes off in the form 

 of an invisible gas, and the carbon is retained 

 and combined with the sap already formed, 

 and is carried with this to the formative ves- 

 sels which are at work in the plant. Thus, 

 particle by particle, the vessels of plants ob- 

 tain from an invisible gas, the material of 

 which their structure is chieHy formed. That 

 the structure of plants is chiefly composed of 

 carbon, we may determine by examining a 

 piece of charcoal, after everything else has 

 been driven off by heat. We find that it con- 

 sists of nearly pure carbon, and retains the 

 form and nearly the size of the plant. 



Animals feed on materials that have been 

 organized in the vessels of plants. They have 

 not the power of assimilating and vitalizing 

 inorganic mineral matter. But plants feed on 

 dead inorganic matter. They have the power 

 of assimilating and appropriating to their own 

 use, material derived from the mineral king- 

 dom. The amount of material annually or- 

 ganized into the structure of vegetables on the 

 surface of the earth, is inconceivably great. 

 Whence is it obtained ? From what sources 

 derived.-^ I answer, from the air and from 

 water. Pure atmospheric air consists of oxy- 

 gen and nitrogen. But air is not pure as it is 

 presented to plants. It contains various sub- 

 stances in solution ; substances which may be 

 said to be accidental to it, which are not essen- 

 tial to its constitution, and may therefoi-e be 

 withdrawn from it without injury. These sub- 

 stances are collected into the atmospheric 

 ocean, by which all ])lants are constantly bath- 

 ed, and stored there for their use. About one 

 thousandth pai't of the atmosphere is carbonic 

 acid. This is returned to the atmosphere by 

 the decay and combustion of vegetable and 

 animal matter ; by the respiration of animals, 

 and by the decomposition of minerals, as fast 

 as it is withdrawn by the growth of vegetables, 

 so that the balance is never greatly disturbed. 

 Carbonic acid gas is somewhat heavier than 

 common air, and tends to accumulate in the 

 lower strata of the atmosphere. Thus we find 

 it in valleys, pits and wells. This circumstance 

 brings it within reach of plants. But it is in- 

 capable of sustaining animal life, and the sim- 

 ple fact that carbonic gas is heavier than at- 

 mospheric air, would cause all animal life to 

 cease from the earth, had not some compensa- 

 tion been found. This compensation consists 

 in the withdrawal of this gas from the air, by 

 the vessels of growing plants. As we ascend 

 into the atmosphere, carbonic acid is less abun- 

 dant. Perhaps this is one reason why plants 

 thrive with less vigor in elevated situations. 



