LYGINODENDRON 381 



down to perhaps one-tenth of the diameter in the case 

 of minute rootlets. 



The roots branched freely ; their lateral appendages 

 are always rootlets, i.e. the branches are decidedly 

 smaller than the parent organ ; their branching was thus 

 monopodial, as in Ferns or Cycads, not dichotomous, as 

 in Lycopods. The rootlets were of endogenous origin, 

 and their xylem is always in connection with one of the 

 protoxylem-angles of the main root (see Fig. 141, rt). 

 In these points, as in all others, the morphological 

 character of these organs, as typical roots, is manifest. 



Cases have recently been observed, by Professor F. E. 

 Weiss and others, in which the structure of the root- 

 apex is perfectly preserved. Details have not yet been 

 published, but it appears that the growing point, unlike 

 that of most Fern-roots, had no definite apical cell. 



All the larger roots show, if old enough, well-marked 

 secondary growth. Every stage of the process has been 

 observed, showing that it took place exactly in the 

 manner characteristic of the roots of Gymnosperms 

 and Dicotyledons at the present day. The cambium 

 first arose by the division of conjunctive cells, lying 

 immediately within the phloem-groups. The isolated 

 cambial arcs thus formed were next united into a 

 continuous zone, by the division of pericyclic cells 

 lying outside the protoxylem-angles. Opposite each of 

 these angles a principal ray was formed, and thus the 

 secondary vascular tissue was at first broken up into 

 distinct bundles, corresponding in number and position 

 to the primary groups of phloem (see Fig. 141, which 

 shows the secondary tissues at a rather early stage of 

 development). Subsequently, the principal rays became 



