LAWS OF VEGETATION. 73 



as blue vitriol, the solution is taken up into the stem ; but we 

 know not that any solutions injurious to the plant do enter into 

 its circulation, unless like corrosive sublimate they first destroy 

 the spongioles. 



The labor of the cultivator is to be almost wholly expended 

 on the root. The root and its relations should be his chief 

 study. He can affect the plant but little in any other way. 

 The winds of heaven laden with moisture, and which affect the 

 leaf, blow as they have blown, and for field crops the cultivator 

 has little control over them. Equally beyond his control are 

 the gentle showers and the drenching rain. But the condition 

 of the root is more completely in his hands ; lie can place proper 

 ingredients for food around it in the soil ; he can regulate the 

 quantity of water by irrigating, ditching, subsoiling and hoeing. 

 If the soil is too stiff to fit his plant, he can loosen it ; if too 

 light, he can supply clay till it suits him. 



Water holding saline substances in solution, constitutes 

 seventy, eighty and ninety per cent, of the green plant and 

 may be dried out of it. It circulates through every part of it 

 — in the stem, the root and the leaf. This circulating fluid 

 answers the same purpose in the plant that the blood does in 

 the animal, or the rivers and canals do in the body politic, to 

 transport food from member to member. The root, the stem, 

 the leaf are essentially composed of cells, round or square, or 

 hexagonal in the softer parts, but in the firmer parts elongated 

 into hollow fibrous tubes, closed at each end and beveled to 

 each other. It is in these that all assimilation takes place, that 

 the food is changed into the substance of the plant, that water 

 and carbon are changed into gum, and sugar, and starch, and 

 resin, and volatile oils, and organic acids ; for Nature has away, 

 unknown to the chemist, of making all these substances, how- 

 ever different, from the same ingredients, water and charcoal. 

 The plant grows by the multiplication and enlargement of these 

 cells. At first they are a transparent vesicle or sac filled with 

 fluid. In some, this fluid can be seen to circulate around the 

 walls, up one side, down the other, bearing little particles of 

 organized matter. The sap does not circulate in tubes as the 

 blood does in animals, but it goes from cell to cell, passing 

 through their membranaceous walls as liquids of different densi- 

 ties will circulate through a piece of bladder. As the sap 



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