198 



BOTANY AND PHARMACOGNOSY. 



"lateral branches" or "lateral roots" (Fig. 109), hence it is 

 frequently referred to as the " rhizogenous layer/' 



Inside the pericambium (by some authors compared with the 

 pericycle of the stem) we find strands of leptome (P) alternating 

 radially with a corresponding number of strands of hadrome (X). 

 The number of these strands vary in the different groups of plants 

 (Figs. 109, 193, 217, 220), being highest in the monocotyledons 

 where a pith is developed, as in sarsaparilla (Fig. 193), several 

 grasses, palms, etc. This peculiar arrangement of the leptome 

 and hadrome, as separate strands alternating with each other, 



B 



Fig. 108. A, longitudinal section through the apical region of the stem of the embryo 

 of a bean (Phaseolus multiflorus) ; ss, apex; pb, parts of the two first leaves, and their 

 axillary buds (k, k,); r, periblem or primary cortex. B, diagram of longitudinal section 

 through winter bud of Qucrcus coccinea: P, growing point; L, young leaves; SB, stem 

 branches; F, fibro vascular bundle. A, after Sachs. 



and not being located, as in stems, in the same radii, has given 

 rise to several adverse views. Some authors have considered 

 the root-stele as one single mestome-strand (or fibrovascular 

 strand), while others especially of recent date compose the struc- 

 ture with that of several mestome strands, and of the hadro- 

 CENTRic TYPE where the leptome partly surrounds the hadrome.^ 



' Compare Kattein : Der Morphol. Werth d. Centralcylind. d. Wurzel. 

 Cassel, 1897. 



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