EQUISETINEAE. 



265 



also like the buds are not always developed ; they are produced sometimes even on 



aerial nodes in moisture and darkness, and from lateral buds on the nodes (compare 



Fig. 220). The apical cell of the root is seen in the lower part of the lateral 



buds, and in E. arvetise these are the only adventitious roots that are produced. 



The buds on the underground parts of stems 



usually disappear when they have produced 



a root. In the lower part of the stem, the 



rhizome, of E. limosum are found buds which 



develope from one to six roots, the rhizo- 



genous buds of Janczewski ; with them are a 



few others which become vigorous branches 



or stems. In these rhizogenous buds the 



growing point of the branch is arrested in its 



development. 



The mode of growth of the roots is in 

 its earliest stages essentially the same as in 

 the roots of Ferns, as is represented diagram- 

 matically in Fig. 220 ^ The cortical tissue is 

 differentiated into an inner and an outer layer ; 

 the former gives rise to air-conducting inter- 

 cellular spaces, which like the cells them- 

 selves are at first disposed in radial and 

 concentric row's, and afterwards unite by rup- 

 ture of the cells into a large air-space sur- 

 rounding the vascular bundle. In the forma- 

 tion of the vascular bundle of the root, three 

 only of the six primary cells which compose 

 the rudiment of the bundle as seen in trans- 

 verse section, the three, namely, which extend 

 to the centre, are each at first divided by 

 a tangential (periclinal) wall, so that the ru- 

 diment of the bundle now consists of three 

 inner and six outer cells; the six outer cells 

 produce a cambial tissue, in which the forma- 

 tion of vessels begins from two or three points, 

 and proceeds inwards ; at length one of the 

 three inner cells produces a wide central 

 vessel; phloem forms in the circumference 

 of the bundle. While in the other Vascular 

 Cryptogams the innermost layer of the cortical 

 tissue becomes the bundle-sheath, the radial 



walls of the cells showing the characteristic folding, in the roots of the Equi- 

 setaceae it is the layer next outside the innermost layer which has this peculiarity ; 



Fig. 220. Diagram of the succession of cell-division 

 in the tip of the root of Eqiiisetiint hiemale ; the diagram 

 serves also in the main for the Ferns and for Marsilia. A 

 longitudinal section. B transverse section at the lower 

 end of A ; h, h, k the primary walls, j, s, s the sextant 

 walls of the segments indicated in A by the figures / to 

 Jry/, /{•, /, m, II, q the layers of the root-cap omitting all 

 further divisions ; f, c denotes the walls in the substance 

 of the root which separate the primordial vascular bundle 

 from the cortex, e the boundary-wall between the epidermis 

 and the cortex, r r the boundary-wall between the outer 

 and inner cortex ; i, 2, 3 the successive periclinal walls, by 

 which the inner cortex is divided into several layers, the 

 radial divisions being omitted. After Nageli and Leitgeb. 



» The curvature and junction of the walls is not quite correctly given in the figure, as will be 

 seen by comparison with Fig. 193. 



