58 VASCULAR CRYPTOGAMS 



dermatogen and periblem, the rudiments of the ' vascular ' bundle 

 penetrating nearly to its apex. In some species it projects in the young- 

 est leaves in the form of a low cone ; in others the apex is flat. As in 

 Flowering Plants, the leaves and rudiments of the shoots do not arise 

 from single cells, but from groups of cells which include both the outer- 

 most and the subjacent layers of the primary tissue of the growing point. 



The branching of the stem of Lycopodium is either monopodial or 

 dichotomous in its origin ; but in the latter case one of the bifurcations 

 usually greatly exceeds the other in vigour of growth. The branches 

 are never placed in the axils of leaves, as in Flowering Plants, but 

 usually arise from the stem above a leaf, but without any definite rela- 

 tion to it. In several species two new'growing points of equal strength 

 appear side by side on the flat apical surface, and continue to de- 

 velop dichotomously. In others the rudiment of the new branch takes 

 the form of a lateral protuberance on the greatly elevated cone of 

 growth. On the stems of many species the small leaves are so closely 

 packed that the internodes are completely suppressed. 



The internal structure of the stem of Lycopodieae presents several 

 peculiarities. The cells of the fundamental tissue are sometimes 

 uniformly thin-walled, but usually the inner layers in particular have 

 thicker walls, and the cells are prosenchymatous, or even have their walls 

 strongly sclerotised, reminding one of the sclerenchymatous layer in 

 ferns; but they are never coloured brown. The axial ' vascular ' cylinder 

 is separated from the cortical fundamental tissue by a strongly developed 

 bundle-sheath, composed of from one to three layers of cells. Air- 

 cavities and mucilage- and gum-passages sometimes occur in the funda- 

 mental tissue of the stem and the leaves. The ' vascular ' bundles them- 

 selves present a striking peculiarity in Lycopodium, forming in the stem 

 and root a single axial cylinder, usually with a circular outline. In this 

 compound bundle are plates or bands of xylem, which are either com- 

 pletely isolated, or coalesce in various ways so as to form figures which 

 are divided into two similar halves by an axial longitudinal section. The 

 cylinder may therefore be described as displaying a bilateral symmetry. 

 If transverse sections are made at different heights in the stem, the 

 xylem presents different figures, in consequence of the bands anasto- 

 mosing in their course. The elements of these xylem-bands are, like 

 those of ferns, tracheides pointed at both ends, and increasing in breadth 

 towards the interior, the most common form of thickenirtg being pitted 

 or scalariform rather than annular or spiral ; the latter are found only 

 at the outer edges of the bands. The whole mass of xylem-bands is 

 surrounded by a narrow-celled phloem, containing, in the larger species, 

 sieve-tubes. Between the outer edges of the xylem-bands and the 



