504 
' R. J. HARVEY-GIBSON AND ELSIE HORSMAN ON 
The predominance of stereome and the reduction in the number of conductive 
elements is to be correlated with the xerophytic character of the plant. The 
small amount of leaf surface, and the consequent reduction in transpiration, the 
necessity for protecting the cell contents from the intense insolation to which 
Berberis is subjected in its native habitats (Asia, South and Central America), 
may also be associated with the predominance of sclerosis and the large develop- 
ment of wood fibres. 
Broad primary , medullary rays persist, and consist of markedly sclerotic ceils 
which, in transverse section, closely resemble the xylem elements^ but are often 
larger than the adjacent xylem fibres. The rays are three or four cells wide, and 
the cells have rounded ends. They are elongated radially, the radial diameter 
being in many, cases almost twice the tangential one. All the walls show numerous 
simple pits, and most of the cells are well filled with starch grains during the 
winter. No secondary rays are produced. The contents of the medullary ray 
regions of the cortex have been previously described. 
The medulla is heterogeneous ; the cells near the protoxylems are smaller than 
the rest and -have well-thickened walls. They show nuclei when young, and starch 
grains in the winter condition at all ages. Numerous simple pits occur on all their 
walls. The central cells are larger and become polygonal by mutual pressure ; they ' 
are thin-walled and devoid of contents. 
The petioles are slender and wiry. In the main portion of the petiole there are 
four vascular bundles surrounded by sclerenchyma, but these unite as the lamina 
is approached. In the basal region there are only three vascular bundles, which 
later on divide into four. As the petiole expands into the lamina the vascular 
bundles again rearrange themselves into three bundles. 
Other Species of Berberis. 
Most of the species of Berberis exhibit features similar to those described for 
Berberis vulgaris , among which the following structural variations may be noted. 
Spines occur on the stems of some species. They are outgrowths from single 
epidermal cells, and are present in B. Yunnanensis, Franch., B. stenophylla x hort., 
B. angulosa, Wall., B. Wallichiana, DC., B. empetrifolia , Lam., and B. Darwinii, 
Hook. (fig. 6). In the last-mentioned species they are much longer, are curved, and 
have transverse partitions. 
The sub-epidermal parenchyma in B. aristata, DC., B. stenophylla x hort., 
B. empetrifolia , Lam., and B. aquifolium, Pursh., shows foldings in the cell walls 
as described for Corydalis raeemosa (l), but in the present instances the folding 
appears to be caused by the pressure of internal tissues acting in opposition to the 
resistance offered by the epidermis. In the older stems the compression increases 
until these cells are cast off along with the other, tissues external to the deeply- 
seated cork. 
