Vegetable Physiology. 119 



a leaf, or even a fragment of a leaf, or a piece of a stem, is 

 sufficient to indicate with certainty whether the plant to which 

 it belonged had one cotyledon or two, whether it had pith, wood 

 and bark, or none of these, and whether it increased by inter- 

 nal or external additions. 



We are now ready to proceed to the examination of the five 

 essential organs of plants, the parts of which they are com- 

 posed, and their uses in vegetable economy. The structure 

 and functions of the Root are of primary importance. The 

 Root may be defined as that part which terminates the plant 

 below, and penetrates into the soil. It generally consists of 

 two parts, the caudex, or body, and the radicles, or fibres. 

 These latter are terminated by soft, succulent extremities, 

 called spongioles, which, as we shall see, perform an important 

 office. Upon the roots the plant is dependant for the supply 

 of moisture required for its growth. That they actually absorb 

 a great amount of fluid matter, may readily be proved by 

 placing those of almost any plant in a tumbler of water. It has 

 been found that four plants of spearmint, weighing altogether 

 four hundred and three grains, have taken up in fifty-six days 

 fifty-four thousand grains, or almost seven pints, of water. The 

 greater part of this is exhaled from the leaves, by a process 

 hereafter to be mentioned, and only a small proportion is 

 retained as food for the plant. This great supply of fluid 

 appears to be necessary in order to aflbrd the plant a suffi- 

 ciency of the solid matter which it also requires, and which is 

 contained in the liquid in very minute proportions. In some 

 plants, as the sea-weeds, this power of absorption is not con- 

 fined to the root, but belongs to the whole surface. Upon 

 examining the root of a Rose, it will be found to branch and 

 spread beneath the ground, in much the same way as the 

 branches above. From the sides and extremities of the prin- 

 cipal divisions proceed delicate fibres, each terminated with its 

 spongiole. That the fibres are the parts by which alone 

 absorption takes place, can be readily proved. If a radish be 

 taken from the ground, while growing, and the root be so bent 

 that it can be covered with water, and the leaves, and the 

 fibres at the point of the root, be kept dry, the plant will soon 

 wither. But if only the points of the fibres be allowed to 



