464 VASCULAR CRYPTOGAMS. 



and annoitnum and of the creeping shoots of L. inundatum; yet it arises in such 

 a manner that the branching maj' be regarded as being closely allied to dichotomy. 

 The bifurcation of the fertile branch of L. alpinum presents another form of 

 dichotomy (false dichotomy), for here the growing-point is extended by the develop- 

 ment of two new growing points, one on the right and the other on the left side of 

 it; the central one then ceases its activity, whereas that of the two lateral ones 

 commences, so that the apex of the parent shoot becomes indistinguishable. Those 

 Lycopodieae which have their leaves arranged in four rows, and which resemble the 

 Selaginelleae (Z. complanaium, chamcEcyparissus)^ branch in one plane only, which 

 coincides with that of^the larger leaves; whereas those species which have their 

 leaves arranged spirally or in whorls, branch in various intersecting planes. Hegel- 

 maier recognised the bulbils which occur in several species (Z. Selago, lucidum, 

 reflexuni) as being peculiarly modified branches. They arise on the shoot in the 

 place of leaves. They fall off of themselves, and are provided with a few leaves and 

 a rudimentary root. 



Since the leaves are closely placed by the side of and above each other from the 

 first, so as to cover the whole surface of the stem, there are no internodes (as also in 

 Ophioglossum, Marattia, Aspidium, Isoeies) ; and not only so, but the outer cortical 

 layer of the stem is genetically connected with the tissue of the bases of the leaves. 

 The leaves become separated the one from the other by subsequent intercalary 

 growth, and in many cases the base of the leaf becomes sharply defined from the 

 stem. 



The first rudiments of the leaves of Lycopodiese appear as multicellular lateral 

 protuberances of considerable breadth upon the growing apex of the stem. They 

 grow at first apically, but this soon terminates in the formation of a hair-like 

 prolongation ; all further growth is intercalary at the base of the leaf. The size and 

 form of the leaves are very different in the various species, but they are always 

 simple unbranched, and not stalked but sessile with a narrow base. Occasionally 

 their surfaces, with the exception of the free apices, are closely applied to the stem 

 (as is the case in Thuja), but more commonly the leaves are quite free. They are 

 acicular, or at any rate of small width, and, as in all Dichotomeae, a mid-rib only and 

 no lateral veins is present. 



The phyllotaxis is sometimes verticillate, sometimes spiral, and both kinds may 

 occur on the same plant. The whorls may consist of pairs of leaves which 

 decussate, or of three, four, or more, and are arranged in creeping stems on zones 

 the planes of which are oblique to the long axis of the stem. The number of leaves 

 in a whorl varies even on the same shoot. According to Hegelmaier, the whorls are 

 true ones ; the leaves composing them are developed simultaneously and at the same 

 level at the puncium vegetaiionis. Where the phyllotaxis is spiral it is so from the 

 first, and the divergence undergoes no important modification. The small and very 

 various divergences of the leaves are remarkable, as Braun pointed out ; he found in 

 Z. clavatuvi the following divergences, f , y^j, ^^^ y^g-, y2_^ as well as whorls consisting 

 of from four to eight leaves ; in Z. annotinum they were f , f , and whorls of four or 

 five leaves; in Z. inundatum f and whorls of five leaves (Bot. Zeit. 1872, p. 815). 



The much bifurcated, multiangular, thin stem of Psilotum grows by means of 

 a three-sided apical cell, which, according to Nageli and Leitgeb, forms (in the 



