198 



BOTANY AND PHARMACOGNOSY. 



sion, and constitute the tissue known .as primary meristem. In 

 the root three kinds of primary meristem (Fig. 60) are distin- 

 guished: (i) The PLEROME {m, f, g) or axial meristem, which 

 gives rise to the central cylinder or stele; (2) the periblem {x, r) 

 or meristematic tissue, which gives rise to the primary cortex, 

 and (3) the dermatogen {e), from which the epidermis is devel- 

 oped. In addition to these three meristematic zones thfere is at 

 the apex, lying next to the dermatogen, a meristematic group of 

 .cells which give rise to the root-cap, known as the calyptrogen 

 is). 



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 Quercus coccinea: P, growing point; L, young leaves; SB, stem 

 branches; F, fibrovascular bundle. — A, after Sachs. 



At the growing point of the stem three meristematic zones are 

 also distinguished, namely, plerome, periblem and dermatogen 

 (Fig. 108, A). They are not, however, so well marked as in the 

 case of roots. 



The tissues which are developed from the primary meristems 

 constitute the primary structure (Fig. 60). With the growth 

 in thickness of the stems and roots of Dicotyledons other meri- 

 stematic cells known as secondary meristems arise. These are 

 of two kinds : ( i ) one which gives rise to the xylem and phloem, 



