STRUCTURE OF THE LEAF. 245 



erallj of silicic acid, with lime, potash, soda, phosphoric acid, 

 sulphuric acid, chlorine, &c. Now, then, we find at last that 

 in a chemical form we have in the soil precisely the same 

 materials that we find in the ash of the plant which we 

 burned; and it is possible that although these minerals are 

 as indestructible as the rocks (that is just the way to put it), 



— although these materials are just as indestructible as the 

 "rocks, yet it is possible that this plant, somehow or other, 



contrived a way to draw lime, potash, and phosphoric acid 

 out of the rocky materials of the soil. Let us, then, go back 

 to the plant, and commence another examination. 



The feeding-organs of the plant, we read, are the leaves 

 and the roots. We will examine first the leaves. Now, this 

 leaf is curiously and wonderfully made. First, it has a 

 frame-work, which we call the ribs of the leaf. Through 

 the centre, comparatively speaking, is one large timber, made 

 of curiously-compacted fibrous material, connected with the 

 stem of the leaf, and by the stem with the cambium of the 

 plant from which it grows ; branching out on the right hand 

 and the left are ribs or timbers of smaller dimensions, 

 strongly built in all directions ; and over the whole, both 

 above and below, is di-ax^Ti the epidermis, or skin-cover, or 

 coating, incasing and enclosing the frame-work of the leaf. 

 Now, between the two, we find an open-work of cells, — cells 

 that are cavities within the leaf, and yet are capable of hold- 

 ing air, gas, and water. Examining now the epidermal coat- 

 ing of the leaf, we find this curious fact, that every leaf is 

 covered with a fine net-work of something which resembles 

 hairs, and beneath that, or connected with it, a material 

 which resembles wax, which completely, perfectly excludes 

 from the inside of the leaf every thing solid and every thing 

 liquid. Through that part, then, we know that nothing 

 entered tliis leaf that was either in a solid or in a liquid 

 state, because the surface of the leaf is perforated only by 

 the most minute microscopic pores, so fine, that on a single 

 apple-leaf there are hundreds of thousands of these little 

 orifice •. entering from that to the cellular work within. 



If tliis leaf, then, is one of the feeding-organs of the plant, 



— and all leaves in this respect are alike, — if this leaf is one 

 of the feeding-organs of the plant, it has gathered nothing, 

 it never can gather any thing, it never can feed upon any 



