XIII 



LYCOPODINE^ 



499 



The roots always normally branch dichotomously, as in 

 Isocfcs, and the successive divisions usually are in planes at 

 right angles to each other. As in Isoctcs, the process is in- 

 augurated by a broadening of tlie apex of the root, which is 

 followed by a forking of the plerome and a subseriuent division 

 of the other histogenic tissues. 



The structure of the mature root (Russow (i)) in L. 

 clavaHun, L. alpijiiini, and 

 most species examined, is ^ 



much like the stem. The 

 hexarch to decarch fibrovas- 

 cular cylinder is radial in 

 structure, the xylem plates 

 often united at the centre, so 

 that in cross-section they 

 present a more or less regu- 

 lar stellate form. In L. 

 selago and L. uiiindatum, 

 according to Russow, the 

 xylem is diarch and the two 

 masses united into a single 

 one, which is crescent-shaped 

 in section, with the phloem 

 occupying the space between 

 the extremities. As in the 

 stem the primary tracheids 

 are narrow annular and 

 spiral ones, and the large 

 secondary ones scalariform. 



Geimncu 



Fig. 289. — A, End of a shoot of Lyco- 

 podium lucidiilum, with gemmae 

 (k) and sporangia (sp) , X2; B, a 

 single bulblet, X4; C, germinating 

 bulblet of L. selago (after Cramer), 

 Xa; r, the primary root. 



Special bulblets or gem- 

 mae are formed regularly in 

 a number of species of Ly 

 copodimn, and have been 

 the subject of several special 



investigations (Cramer (i); Hegelmaier (i); Strasburger 

 (7)). These in L. hicidnlum (Fig. 289, A, k) are flattened, 

 heart-shaped structures composed of several thickened fleshy 

 leaves, and formed apparently in the axils of somewhat modi- 



