LESSON 26.] PRODUCING ORGANIC MATTER. 163 



do decompose carbonic aei«r in their leaves and give out its oxygen, 

 — by the experiment mentioned in paragraph 461. ; %^g^ the 

 leaves, as we have stated, are taking in carbonic aeid' gas. We 

 now add, that they are giving ,out oxygen gas at the same rate.- 

 The air as it comes from the glass g^o^^ J^J^JJ"^^ \^&y^ just as 

 much more oxygen as it has less carbonic aei^tnan before — just 

 as much more oxygen as would be raquiredAo turn the carbon re- 

 tained in the plant back into carboifK^ia-agam. 



469. 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 .^fryrA, 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. 57 - 60) ; or in subter- 

 ranean stems or branches, as in the Potato (Fig. 68), and many 

 I'ootstocks ; or in the bases of leaves, as in the Onion, Lily (Fig. 

 73-75), and other bulbs ; or in fleshy leaves above ground, as those 

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

 the whole thickened body, as in many Cactuses (Fig. 76) ; 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), Bean (Fig. 16), Pea (Fig. 19), &c. In all these' 

 forms this is a provision for future growth, either of the . plant 

 itself or of some offset from it, or of its oflEspring, 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 shaped and consolidated. It has exactly the 

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

 ejementa' of water, by decomposing . the same amount of carbonic 

 ^effancrgiving back its oxygen to the air. In using it for growth, 

 the plant dissolves it, conveys it to the growing parts, and consoli- 

 dates it into fabric. 



470. Sugar, another principal vegetable product, also has essen- 



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

 . same common food of plants, with the same result. The different" 

 kinds of sugar (that of the cane, &c. and of grapes) consist of the ' 

 same three materials as starch and cellulose, only with a little more 

 water. The plant generally forms the sugar out of starch, changing 

 one into the other with great ease; starch being the form in which 

 prepared material is stored up, and sugar that in which it is ex- 



