FOOD OF PLANTS 21 



The soil is also the source whence plants derive their sa- 

 line, earthy, and metallic ingredients. The silica they often 

 contain is, in like manner, conveyed to them by the water, 

 which it is now well ascertained, by the researches of Ber- 

 zilius, is capable of dissolving a very minute quantity of this 

 dense and hard substance. It is evident that, however small 

 this quantity may be, if it continue to accumulate in the 

 plant, it may in time constitute the whole amount of that 

 which is found to be so copiously deposited tm the surface, 

 or collected in the interior of many plants, such as the bam- 

 boo, and various species of grasses. The small degree of 

 solubility of many substances thus required for the con- 

 struction of the solid vegetable fabric, is, probably, one of 

 the reasons why plants require so large a supply of water 

 for their subsistence. 



2. Absorption of Nutriment by Plants. 



THE greater number of cellular plants absorb water with 

 nearly equal facility from every part of their surface: this is 

 the case with the /^a?,for instance, which are aquatic plants. 

 In- Lichens, on the other hand, absorption takes place more 

 partially; but the particular parts of the surface where it oc- 

 curs are not constantly the same, and appear to be deter- 

 mined more by -mechanical causes than by any peculiarity 

 of structure: some, however, are found to be provided in 

 certain parts of the surface with stomata, which De Can- 

 dolle supposes may act as sucking orifices. Many mush-* 

 rooms appear to be capable of absorbing fluids from all parts 

 of their surface indiscriminately; and some species, again, 

 are furnished at their base with a kind of radical fibrils for 

 that purpose. 



In plants having a vascular structure, which is the case in 

 by far the greater number, the roots are the special organs 

 to which this office of absorbing nourishment is assigned: 

 but it occasionally happens that, under certain circumstances, 

 the leaves, or the stems of plants are found to absorb mois- 



