EQUISETACE^. 



36: 



The end of the stem enveloped by a large number of younger leaf-sheaths 

 terminates in a large apical cell, the upper wall of which is arched in a spherical 

 manner, while below and at the side it is bounded by three almost plane walls. 

 The apical cell has therefore the form of an inverted triangular pyramid, the 

 upturned basal surface of which is a nearly equilateral spherical triangle. The 

 segments are cut off by walls which are parallel to the oblique sides of the apical 

 cell, that is, to the youngest primary walls of the segment ; the segments, disposed 



FIG. 273.—^ ongitudinal section of the end of a stem in an under^ound bud of Equisetum Tehnatein ; S apical cell, xy first 

 indication of the girdle from which the leaves are subsequently formed, b b s. more advanced and distinctly marked foliar 

 girdle, bs the apical cells of a strongly projecting foliar girdle, rr rudiment of the cortical tissue of the internodes, gg rows 

 of cells from which the leaf-tissue and its fibro-vascular bundle proceed, zzthe lower layers of cells of the segment which take 

 no part in the formation of leaves (from nature) ; B horizontal projection of the apical view of the end of a stem of E. Telmateia ; 

 s apical cell, /— Kthe successive segments, the older ones still further divided; C horizontal projection of the apical view of 

 E. a-rvetise; D optical longitudmal section of the end of a very slender stem ; E transverse section of the end of a stem after the 

 formation of the vertical and first tangential walls. (C, D, E, after Cramer; the Roman numerals indicate the segments, the 

 Arabic numerals the walls formed in them in the order of their succession ; the letters the primary walls of the segments.) 



in a spiral \ arrangement, lie in three vertical rows. Each segment has the form of a 

 triangular plate with triangular upper and under walls, rectangular lateral walls lying 

 right and left, and an outer rectangular wall which is curved. Each segment is first 

 divided— as was shown by Cramer and Rees and confirmed by myself— by a wall 

 parallel to the upper and under surfaces into two equal plates lying one above 

 another, and consequently each half the height of the undivided segment. Each 



