398 
VASCULAR CRYPTOGAMS. 
been mentioned, disposed originally in a spiral with ^ arrangement ; and since 
each segment without exception (as in Mosses) produces a leaf or what corresponds 
to a part of a leaf-sheath, the leaves of Eqidsetum must also be arranged in a 
spiral. This does, in fact, sometimes occur when the growth is abnormal ; but 
when the growth is normal, a small displacement takes place at a very early 
period, of such a nature that the three segments which form a cycle always 
come to be arranged into a disc transverse to the stem, their outer surfaces thus 
Fig. 279.— /^ longitudinal section of the end of a stem in an underground bud of Equisetiim Telmateia ; S apical cell, xy first 
indication of the girdle from which the leaves are subsequently formed, b b 2. more advanced and distinctly marked. foliar 
girdle, bs the apical cells of a strongly projecting foliar girdle, r rudiment of the cortical tissue of the internodes, rows 
of cells from which the leaf-tissue and its fibro-vascular bundle proceed, z z' the 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 if. Telmateia; 
s apical cell, / — /^the successive segments, the older ones still further divided ; C horizontal projection of the apical view of 
E. arvense; D optical longitudinal 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.) 
forming an annular zone or girdle. According to Reess, to whom this observation 
is due, the three segments of each cycle are formed in rapid succession, while 
a longer time elapses between the formation of the last segment of the preceding 
and that of the first of the succeeding cycle. Thus by the unequal growth of 
the segments in longitudinal direction each cycle of segments or turn of the 
spiral produces a whorl, which therefore, strictly speaking, is a pseudo-whorl, 
because resulting from subsequent displacement. Each whorl of segments now 
