LKSSON 20.] PROnrHNO OKGANIC MATTEU. 163 



do decompose carbonic acid in tlicir loaves and give out its oxygen, 

 — by the experiment mentioned in paragraph 4(51. There tlie 

 leaves*, as we have stated, are taking in carbonic a<-id gas. A\'e 

 now add, tliat tliey are giving out oxygen gas at the same rate. 

 The air as it comes from the glass globe is tbund to have just us 

 much more oxygen as it has less carbonic acid than before — just 

 as much more oxygen as would be inquired to turn the carbon re- 

 tained in the plant back into carbonic acid again. 



4('>'.). It is all the same when plants — instead of making fabric at. 

 once, that is, growing — make the prepared material, and store it 

 up for future use. The principal product of plants for this purpose 

 is Starch, which consists of minute grains of organic matter, lying 

 loose in the cells. Plants often accumulate this, perhaps in the root, 

 as in the Turnip, Carrot, and Dahlia (Fig. o7 - GO) ; or in subter- 

 ranean stems or branches, iis in the Potato (Fig. ^'6), and many 

 rootstocks ; or in the bases of leaves, as in the Onion, Lily ( Fig. 

 7<5 — 75), and other bulbs ; or in fleshy leaves above ground, as those 

 of the Ice-Plant, Ilouse-leek, and Century-Plant (Fig. 82) ; or in 

 the whole thickened body, as in many Cactuses (Fig. 70); or in 

 the seed around the embryo, as in Indian Corn (Fig. 38, 39) and 

 other grain ; or even in the embryo itself, as in the Horsechestnut 

 (Fig. 23, 24), Ik-an (Fig. 10), Pea (Fig. 10), &c. In all these 

 ibnns tliis is a provision for future growth, either of the plant 

 itself or of some offset from it, or of its oflfspring, as it springs 

 from the seed. Now starch is to cellulose or vegetable fabric just 

 ■what the prepared clay is to the potter's vessel, — the same thing, 

 only requiring to be shajied and consolidated. It has exactly the 

 same chemical composition, and is equally made of carbon and the 

 elem.ents of water, by decomposing the same amount of carbonic 

 acid and giving back its oxygen to the air. In using it for growth, 

 the plant <lissolves it, conveys it to the growing parts, and consoli- 

 dates it into fabric. 



470. Sii(j(ir, another principal vcgetal»le product, also has essen- 

 tially the same chemical composition, and may be formed out of the 

 same connnon food of |)lants, with the same result. The different 

 kinds of sugar (that of the cane, iVc. and of grapes) consist of the 

 panic three m:Uerials Jis starch and cellulose, only with a little more 

 w.itrr. Tiie plant generally forms the sugar out of starch. clianLMii^ 

 one into tiie otlier with great ease; starch being the form in wliich 

 prepared m:U(rial is stored up, and sugar that in wliich it is ex- 



