STRUCTUKE AND GROWTH OF PLANTS. 67 



shows to consist of delicate tubes terminating in a porous 

 sponge-like mass of cellulai* fibre. The pores discovered in 

 the spongy extremities of the root-branches are so exceed- 

 ingly minute, that it is impossible for solid matters, no matter 

 how finely divided, to pass through them. It is, however, 

 by these pores that the living plant is supplied with some of 

 the materials most essential to its existence, and the power 

 which the spongy extremities of the root possess of sucking 

 in the moisture of the soil and the matters dissolved in it, 

 and of conveying it to every part of its structure, is one of 

 the most remarkable phenomena which the study of plants 

 presents. You will now perceive the immense importance 

 of a proper supply of water to vegetable life; dissolved in that 

 useful liquid, the gases, carbonic acid, oxygen, and ammonia, 

 as well as the earthy and saline matters of the soil, can readily 

 be taken up by the plant and employed in its development. 



92. Growth of Plants. After this sm-vey of the parts 

 which constitute the machinery of the plant, let us consider 

 the nature of the changes by which it can within its structure 

 convert the simple materials which it imbibes into the various 

 interesting compounds lately described. 



Development of the seed. As has already been stated 

 (81), a seed when placed in the ground is observed in the 

 course of a short tune to undergo a remarkable alteration, 

 like what is produced by malting barley. It swells up and 

 acquires a sweet taste, and from its interior two portions 

 extend themselves, which gradually increase in size and 

 become the root and stem of the future plant. 



93. In the first stage of its growth the young plant lives 

 at the expense of the matters stored within the seed ; water 

 alone of the materials existing in the atmosphere and the 

 soil contributmg to its development ; and instead of accumu- 

 lating food from the air which penetrates into the soil, a 

 portion of the carbon of the seed enters into combination with 

 the oxygen of the atmosphere and is given off as carbonic 

 acid. In the seed there is laid up a store of starch and 

 gluten, but it will be recollected, that these compounds are 

 insoluble in water (64, 74) and could not therefore enter 

 into the vessels of the young plant: but under the influence 

 of a certain temperature and moisture the gluten undergoes 

 decomposition, and the curious substance diastase, (76) which 

 in the hands of the brewer converts the insoluble starch of 



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