150 FLOWER-GARDENING. 



germinate, and, consequently, an exposure to light is fatal t< 

 their embryo, because (278) oxygen will not be absorbed ii 

 sufficient quantity to stimulate the vital powers of the embryo 

 into action, for the purpose of parting with it again, by the 

 decomposition of the carbonic acid that has been formed dur- 

 ing its accumulation. 



X. SAP. 



260. The fluid matter which is absorbed either from the 

 earth or from the air is called Sap. 



261. When it first enters a plant, it consists of water holding 

 certain principles, especially carbonic acid, in solution. 



262. These principles chiefly consist of animal or vegetable 

 matter in a state of decomposition, and are energetic in pro- 

 portion to their solubility, or tendency to form carbonic acid 

 by combining with the oxygen of the air. 



263. Sap soon afterwards acquires the nature of mucilage 

 or sugar, and subsequently becomes still further altered by the 

 admixture of such soluble matter as it receives in passing in 

 its route through the alburnum or newly formed woody 

 issue (65). 



264. When it reaches the vicinity of the leaves, it is attracted 

 into them, and there, having been exposed to light and air, is 

 converted into the secretions peculiar to the species. 



265. It finally, in its altered state, sinks down the bark, 

 whence it is given off laterally by the medullary rays, and is 

 distributed through the system. 



266. No solid matter whatever can be taken up by the 

 roots ; for this reason, metals, which in the state of oxides are 

 poisonous, are perfectly harmless in their metallic state, as 

 mercury ; and this is, no doubt, the cause why liquid manure, 

 which contains all the soluble parts of manure in a fluid state, 

 acts with so much more energy than stimulating substances in 

 a solid state. 



