106 ELEMENTS OF PLANT ANATOMY. 
named this the initial cell or cells according as there were one 
or several. (Fig. 45.) 
That part of the stem tip lying under the outer layer, is 
composed of a meristematic tissue from whose outer portion are 
produced the cells originating the bundles, while the inner 
layers, or group of cells, give rise to the tissues forming the 
central part of the stem. These inner layers Hanstein named 
ERS 
Ais Ole oo 
OTR KD 
Fia. 45. 
Long section through the tip of stem of Hippuris vulgaris. d dermatogen. per periblem. 
pl plerome. 066'b" beginnings of leaves. x 400.— (decd. to Warming.) 
plerome. ‘They were also supposed to end toward the stem tip 
in a group of initial cells corresponding to those of the dermat- 
ogen layer. So with the layers of cells lying between the 
plerome and the dermatogen, which he named periblem ; these 
too were supposed to terminate in a group of initial cells. 
This interpretation of the order and development of the 
various meristems of the point of vegetation of both stem and 
root was believed to apply to a large number of phanerogams. | 
The examination of a great number of such plants, however, 
has failed to corroborate this opinion. In some cases where 
