28 



MORPHOLOGY OF THE ROOT. 



is similarly capped or protected. 1 But the so-called root-cap is 

 seldom so distinct or separable as to deserve a particular name. 

 45. Nature of Growth, Cells. The development and growth of 

 the root, as of other organs, results from the development, 

 growth, and increase in number of certain minute parts, of which 

 the plant is built up. These component parts are so much alike, 

 at least in an early stage, and are so obviously formed all on 

 one type, that they take one common name, that of CELLS. 

 These are the histological elements of plants, i. e. the units of 

 minute anatomical structure. While, in the morphology of the 

 plant's obvious organs, analysis brings us to the phytomer (16) 

 as the individual element which by a kind of propagation 

 produces its like in a second phytomer, remaining however in 

 connection with the first, thus building up the general structure, 

 so, in an analogous way, each of the obvious parts each stalk 

 or blade or rootlet is microscopically determined to be com- 

 posed of these ultimate organic units, generally called cells. 

 The cell (cellula, by the French 

 conveniently termed cellule) is the 

 living vegetable unit, in the same 

 sense that the brick is the unit 

 of a brick edifice. To make this 

 analogy fairly complete, the 

 bricks should be imagined to 

 have a firm exterior or shell, 

 and a soft or at length hollow 

 _ interior, also to be living when 

 incorporated into the structure, 

 and finally to be produced in the 

 forming structure by a kind of 

 propagation. The production or 

 increase in number of these cells by development from previous 

 ones, and their successive increase in size up to maturity, are 

 what constitutes vegetable growth. 2 The inspection through a 



1 The notion that the tip of the root consists of delicate forming or 

 newly formed tissue, t>r bears some organ or structure of this nature (a 

 " Spongiole "), has hardly yet been eliminated from the text-books and popular 

 writings. It had no proper foundation in fact. 



In Lemna, and in some other aquatics, and also in some aerial roots, this 

 older tissue often separates into a real root-cap, free at base, like an inverted 

 calyptra. 



3 This, as to the structure, is the subject of Histology ; as to processes or 

 actions, the subject of Physiology; both to be treated in a separate volume. 



FIG. 65, 66. Portions of surface of Fig. 64, more magnified, clearly displaying the 

 superficial cellular structure and the long processes from some of the cells, called root- 

 hairs, which abound on the upper part of Fig. 64 



