ANATOMY OF TISSUES. 105 
The manner of growth at the apical regions of phanerogamic 
stems is quite different. That of the stem of Hippuris vulgaris, 
a common water plant, may be taken as an example. ‘This is 
described by Hanstein about as follows. A longitudinal section 
through the axis of the stem tip shows such an arrangement of 
cells as to preclude the possibility of growth from a single apical 
cell. The periclinal curves run very regularly around the tip so 
FIG. 44. 
Point of stem of Equisetum. s apical cell. @outer,i inner meristem. 6 beginnings 
of leaves. X 300. —( Wiesner.) 
as to give the point of vegetation the appearance of being made 
up of separate layers of cells. The anticlinal curves may be 
clearly seen though they are not so regular in their course. The 
entire point of vegetation is here covered with a single layer of 
cells, which with few exceptions divide always by anticlinal, 
never by periclinal walls. If this layer of cells be followed 
down toward the older stem portion, it is found to pass directly 
into the layer which forms the epidermal system. ‘This layer 
of actively dividing cells, covering the entire tip of the stem, 
Hanstein named dermatogen, and claimed that at its summit is 
a cell or group of cells which give rise to and perpetuate it. He 
