LESSON 26.] PRODUCING ORGANIC MATTER. 163 



do decompose carbonic acid in their leaves and give out its oxygen, 

 by the experiment mentioned in paragraph 461. There the 

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

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

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

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

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

 tained in the plant back into carbonic acid again. 



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 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. 57 60) ; or in subter- 

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

 rootstocks ; 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 offspring, as it springs 

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

 what the prepared day 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 carbon and the 

 elements 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 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- 



