EQUISETINEM. 



397 



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 the three infero-lateral walls are almost plane. 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 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 Reess and confirmed by myself — by a wall 

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



Fig. 278. — Eqicisetum Telmateia ; A piece of an upright stem (natural size), i i' internodes, h its central cavity, 

 /lacunae of the cortex, S leaf-sheath, z its apex, a a' a" the lower internodes of young shoots ; B longitudinal section 

 of a rhizome (X about 2), k septum (diaphragm) between the cavities hk, g fibro-vascular bundle, / lacunae of the cortex, 

 ^leaf-sheath; C transverse section of a rhizome (X about 2), ^ and / as before ; Z) union of the fibro-vascular bundle of 

 an upper and lower internode iif. A!" the node. 



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

 lalf-segment is then again halved, in the most usual case, by a vertical nearly radial 

 ^all. The segment now consists of four cells, two of which lie one above the other 



id reach as far as the centre, but the other two do not because the vertical wall is 

 lot accurately radial but intersects one of the lateral walls of the segment (the 

 modal wall), (Fig. 279, E'). Divisions now take place without any strict rule in 

 |jhe four cells of each segment parallel to the primary and the lateral walls; and 



mgential divisions also soon make their appearance, by which the segment is 

 Split up into inner and outer cells, in which further divisions afterwards take place. 



'he former produce the pith, which is soon destroyed as far as the septum at 

 the base of each internode by the expansion of the stem ; the latter produce the 



iaves and the entire tissue of the hollow internodes. The segments are, as has 



