XIV LYCOPODINE^ 473 



The phloem masses are, in the arrangement and develop- 

 ment of the parts, very like the xjdem, and llic formation 

 of the sieve -tubes begins at the outer angles and proceeds 

 centripetally. The fully-developed sieve-tubes appear almost 

 empty, and the small sieve -plates are poorly developed and 

 difficult to demonstrate. 



Where the branching is monopodial, the young branches 

 arise laterally close to the growing point, but without any 

 relation to the leaves. Where, however, as in L. selago} there 

 is a genuine dichotomy, it is inaugurated by an increase in the 

 number of initial cells, which is then followed by a forking of 

 the apex of the plerome cylinder, and the two resulting branches 

 are exactly alike. Intermediate conditions between a perfect 

 dichotomy and true monopodial branching occur. In these 

 there is a true dichotomy, but one branch is stronger than the 

 other, and continues as the main axis, while the weaker one is 

 pushed to one side and looks like a lateral shoot. Bruchmann - 

 has described certain "pseudo-adventive " buds, which are young 

 branches arrested in their development at a very early stage, 

 which may later develop. Strasburger ^ has found adventive 

 buds in L. aloifolimn, L. verticillatiim, L. taxifoliuin, and L. 

 refiexinn, which possibly may be of the same nature. 



The Leaf 



The leaves of all species of Lycopodiiini are relatively small, 

 and are usually lanceolate in outline with broad sessile base. 

 The margins of the leaves are often serrate, and in all cases 

 the leaf is traversed by a simple midrib, which, as already 

 stated, does not reach to the apex. Their arrangement varies, 

 even in the same species, and upon the same shoot. Thus in 

 L. alpimini * the leaves are regularly arranged in pairs which 

 arise simultaneously ; in L. selago they are usually in true 

 whorls of four or five. The latter, however, often shows a 

 spiral arrangement of the leaves, with a divergence of two- 

 ninths, less often two-sevenths. 



The structure of the vascular bundle of the leaf is simple.^ 

 It is concentric in structure, with the central part composed 

 of a small number of spiral and annular tracheids, with the 



^ Strasburger (lo), p. 242. - Luerssen (7), vol. vii. p. 627. ^ Strasburger (7). 



^ Hegelmaier (i), p. S15. ^ Strasburger (11), vol. iii. p. 461. 



