43 



But the root-cap possesses no such function, and it has been 

 shown that it is the part of the root immediately behind the 

 root-cap, i.e., the youngest part of the root, which possesses this 

 power. The epidermal cells which cover this portion grow out, 

 or are prolonged into, certain long thin-walled delicate one-celled 

 hairs, which are the absorptive portion of the root, and which are 

 well seen in the germination of the Garden Cress {Lepidium 

 sativum), and of the Buckwheat {Polygonum Fagopyrum)- 

 The presence of these root-hairs, then, indicates that the 

 cells of that portion of the root are young and capable of 

 absorption; hence, if we find them to be absent, we may usually 

 conclude that the part of the root in question has passed the 

 stage when it could absorb. In certain Coniferae, however, 

 these root-hairs are absent, and absorption takes place in them 

 by the epidermal cells themselves ; also in certain plants, e.g., 

 Utricularia, which float in water, no root hairs are present, but 

 here the cell-walls are unthickened, and the whole surface of the 

 epidermis is capable of absorbing fluid. If we pull up a strongly 

 growing plant out of the ground, the parts of the root which 

 are provided with hairs (neither the extreme apex nor yet the 

 oldest portion) will be seen to be closely covered with earthy 

 particles, which we cannot remove without tearing the hairs. 



The water taken up by the roots from the soil, by a method 

 to be presently described, is not pure, since either rain, or water 

 containing Carbonic Dioxide gas in solution, will act upon the soil, 

 and bring a number of inorganic salts, which are necessary for the 

 nutrition and growth of the protoplasm of plants, into solution 

 in it. Certain other nutritious substances however, required 

 by the plant, are retained by the soil so firmly that water cannot 

 dissolve them out of it. These are decomposed by the acid cell- 

 sap which is contained in the cells of the root, and which 

 saturates even their cell-walls, and they then pass into the plant 

 in the form of salts of organic acids. This we can show by 

 growing a plant in a pot, across which, at a certain height, a 

 plate of polished marble is placed, when we find that the calcic 

 carbonate is decomposed at those parts of the plate which are 

 in direct contact with the roots, and a complete outline of the 



