xiii LYCOPODINEJE 497 



surrounded by a single layer of parenchyma, whose inner cell 

 walls show bordered pits, like those of the adjacent tracheids. 



The phloem masses are, in the arrangement and develop- 

 ment of the parts, very like tlie xylem, and the formation of 

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

 etally. The large sieve-tubes in L. voluhile (Fig. 288, C) are 

 conspicuous, aj^pearing nearly empty, and with delicate, colour- 

 less walls. Upon their lateral faces are numerous sieve-plates, 

 which in the smaller species are not easily demonstrated. 



Where the branching is monopodial, the young branches 

 arise laterally close to the growing point, but without any re- 

 lation to the leaves. Where, however, as in L. selago (Stras- 

 burger fio), p. 242), there is a genuine dichotomy, it is in- 

 augurated by an increase in the number of initial cells, which 

 is then follow^ed by a forking of the apex of the plerome cyl- 

 inder, and the two resulting branches are exactly alike. Inter- 

 mediate conditions between a perfect dichotomy and true mon- 

 opodial 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 "pseu- 

 do-ad ventive" buds, which are young branches arrested in their 

 development at a very early stage, which may later develop. 

 Strasburger (7) has found adventive buds in L. aloifolinm, L. 

 vcrticillatuin, L. taxifolium, and L. rcHexum, which possibly 

 may be of the sarrie nature. 



The Leaf 



The leaves of all species of Lyeopodhim 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, wdiich, 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. alpinum (Hegelmaier (i), p. 815) 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. In other 



species, e. g., L. complanatiim, L. voluhile (Fig. 286, B), the 

 32 



