36 



NEW ENGLAND FARMER. 



Feb. 



CATECHISM 



— F — 



AGRICULTURAL CHEMISTRY AND GEOLOGY. 



BY JAMES P. W. JOHNSTON, M. A. 



[CONTINUED.] 



II. — Of the Organic Food of Plants. 



Q. Do plants require fbd& as animals do? 



A. Yes, all plants require constant supplies of 

 food in order that they may live and grow. 

 j Q. Where do plants obtain their food ? 



A. They obtain it partly from the air and part- 

 ly from the soil. 



Q. Do plants require two distinct kinds of 

 food? 



A. Yes, they require organic food to support 

 their organic part, and inorganic food to support 

 their inorganic part. 



Q. Whence do they obtain organic food? 



A. They obtain their organic food partly from 

 the air and partly from the soil. 



Q, Whence oh they obtain their inorganic food? 



A. They obaiin their inorganic food wholly 

 from the soil in which they grow. 



Q. In what form do plants take in organic food 

 from the air? 



A. In the form chiefly of carbonic acid gas. 



Q. What is carbonic acid gas ? 



A. It is a kind of air which has no color, but 

 has a peculiar smell. Burning bodies are extin- 

 guished in it, and animals die, and it is heavier 

 than common air. It causes the boiling up of 

 soda water, and the frothing of beer, and forms 

 nearly half the weight of all limestone rocks. 



Q. Docs carbonic acid gas form a large part 

 of the atmospheric air ? 



A. No, the atmospheric air consists almost 

 entirely of a mixture of oxygen and nitrogen 

 gases. Five gallons of air contain about four of 

 nitrogen and one of oxygen, but in 5000 gallons 

 there are only 2 gallons of carbonic acid gas. 



Q. Do plants drink in much carbonic acid from 

 the air ? 



A. Yes, they drink in a very large quantity. 



Q. How ran plants drink in so large a quanti- 

 ty of this gas from the air,ichich contains so little? 



A. They -spread out their broad thin leaves in 

 great numbers through the air, and thus are able 

 to suck in the carbonic acid from a large quantity 

 of air at the same time. 



Q. flow do they suck it in? 



A. Bv means of a great number of very small 

 openings or mouths which are spread everywhere, 

 especially over the under surface of the leaf. 



Q. Do the leaves suck in this carbonic acid at 

 all times ? 



No, only during the day time. During the 

 night they give off a quantity of carbonic acid. 



Q. What does carbonic acid consist of? 



A. Carbonic acid consists of carbon, or char- 

 coal, and oxygen. 



6 lbs. of carbon and 16 lbs. of oxygen form 22 

 lbs. of carbonic acid. 



Q. How do you prove this? 



A. By burning charcoal in oxygen gas, when 

 carbonic acid gas will be formed. 



Q. Does the plant retain both the carbon and 

 the oxygen contained in the carbonic acid that is 

 absorbed by its leaves ? 



A. No. it retains only the carbon, Efrving of 



the oxygen again into the air. 



Q. How do you show that the leaves give off this 

 oxygen gas ? 



A. By putting a few green leaves under a tum- 

 bler or gas-rereiver full of water, and setting 

 them out in the sunshine, when small bubbles of 

 oxygen gas will be seen to rise from the leaves, 

 and to collect in the upper part of the tumbler. 



Q. Do the leaves of plants drink in anything 

 else from the atmosphere ? 



A. Yes, they drink in watery vapor. 



Q. What purpose does this vapor serve ? 



A. It serves in part to moisten the leaves and. 

 stems, and partly to form the substance of the 

 plant itself. 



Q. In what form do pjlants take in carbon from 

 the soil ? 



A. In the form of carbonic acid, humic acid, 

 and some other substances which exist in the 

 black vegetable matter of the soil. 



Q. In what forms do plants derive nitrogen 

 from the soil ? 



A. In the forms of ammonia and nitric acid. 



III.— Of the Substance of Plants. 



Q. What does the substance of plants chiefly 

 consist of? 



A. The substance of plants chiefly consists of 

 woody fibre, starch and gluten. 



Q. What is woody fibre ? 



A. Woody fibre is the substance which forms 

 the greater part of all kinds of wood, straw, hay, 

 and chaff, of the shells of nuts, and of cotton, 

 flax, hemp, &c. 



Q. What is starch ? 



A. Starch is a white powder, which forms 

 nearly the whole substance of the potato, and 

 about half the weight of oatmeal, wheaten flour, 

 and of the flour of other kinds of grain cultivat- 

 ed for food. 



Q. What is gluten ? 



A. Gluten is a substance like bird-lime, which 

 exists, along with starch, in almost all plants. It 

 may be obtained from wheaten flour, by making 

 it into a dough, and washing it with water. 



Q. Which of these three substcmces is usually 

 most abundant in plants ? 



A. The woody fibre is the most abundant in 

 the stems of plants, and the starch in their seeds. 



Q. Is starch found in the roots of plants ? 



A. Yes, it exists abundantly in the potato and 

 other similar roots. 



Q. What do u-oody fibre and starch, and also 

 gum cmd sugar consist of? 



A. They all consist of carbon and water only. 



Q. May these substances then be formed from 

 the kinds of food which the leaves drink in from 

 the air ? 



A. Yes, because the leaves drink in carbonic 

 acid and water. 



Q. Can you tell, then, why the leaves give off 

 the oxygen of the carbonic acid into the air ? 



A. Yes, they require only carbon and water 

 to form the woody fibre and starch, of which they 

 consist, and therefore they give off the oxygen 

 of the carbonic acid because they cannot make 

 use of it. 



Q. If plants suck in so much carbonic acid 

 from the air, may they not at length rob the air of 

 the whole of the carbonic acid ti contains ? 



A. No, because new supplies of this gas are 

 continually returning into the air. 



