SOURCES OF NUTRIMENT. 45 



connection with assimilation, nor with one another : the first is a 

 mechanical and the other a chemical process. Thus a cotton wick, 

 in a lamp containing water saturated with carbonic acid, acts like a 

 plant in the night, sucking up both by capillary attraction and evapo- 

 rating them from its upper surface. Plants in a moist situation give 

 off more carbonic acid in the night than in a dry one ; and also more 

 in moist than dry weather. 



Plants yield oxygen in greater quantities than they absorb it. Those 

 growing in the bottom of ditches, etc., are perceived, whilst covered 

 with clear ice, to emit bubbles of oxygen during the day. This they 

 derive from the carbonic acid of the water absorbed by them, and the 

 water is supplied with it by the decayed vegetables in the soil. Oak 

 wood is found to contain an excess of one-twelfth of hydrogen ; in 

 pines the excess is one-seventh, in Tilia and in ebony it is in the pro- 

 portion to form water. The proportion generally is in relation to the 

 weight of the wood ; the lighter kinds containing the most and the 

 heavier the least. 



When seeds are planted and the parts designed for the reception of 

 food are absent, the former are employed entirely in the formation of 

 roots ; each new fibre, and afterwards each new leaf constitutes a 

 ,new mouth, lung and stomach. The functions of the leaves are per- 

 formed at first by the roots ; and they extract carbonic acid from the 

 humus of the seed-soil. Sugar and mucilage in the seeds form the 

 nutriment of the young plant and these disappear during the develop- 

 ment of the buds, leaves and sprouts. The access of air and formation 

 of carbonic acid is favored by loosening the soil. As the humus is 

 absorbed by the roots, it is replaced by the air, which renews the pro- 

 cess of decay and the portions of carbonic acid, till the plant receives 

 food both from above and below, and hastens to maturity. 



The size of a plant, it is affirmed, is in proportion to the surface of 

 the organs destined to convey food to it. When the food is more 

 abundant than the existing organs require, the superfluous nutriment 

 is employed in the formation of new organs ; so that at the side of a 

 cell, a twig or a leaf, arises another. The amount of nutriment re- 

 ceived from the air is in proportion to the extent of the surface of the 

 leaves ; and new developments correspond with this amount. When 

 new products are no longer employed, the nutriment they imbibe goes 

 to the formation of woody fibre and other solid parts. The leaves 

 then produce sugar, starch and acids and when the solids are suffi- 

 ciently extended, the nutriment goes to the production of blossoms. 

 The functions of leaves cease in most plants on the maturity of their 

 fruit and yield to the chemical influence of the oxygen of the air, change 

 their color and fall oft'. Between blossoming and the maturity of 

 fruit, a transformation of the matter of plants takes place and new 

 compounds are formed in the blossoms, fruit and seeds, while other 



