— 238 — 
that a hypoderm in which some cells become bast-cells while 
others remain thin and ultimately disappear leaving empty 
spaces between the bast-bundles. There are 4 or 5 layers 
of palisade cells of which the innermost are bounded by 
a storage-sheath of large thick-walled lignified cells with 
numerous pits. Internal to these are vascular bundles with 
the leptome sheathed by small bundles of bast, while between 
the vascular bundles is a small-celled tissue. The pith is a 
large-celled aqueous tissue. 
Heliotropium sogdianum Bge. 
This species which has been referred to several times in 
the preceding chapters (e. g. p. 123, 124), forms long horizontal 
Fig. 63. Heliotropium (Radula?). Part of a horizontal rhizome with 
aerial shoots. 
subterranean shoots from which aerial shoots arise, some- 
times widely apart. A creeping stem of this type is shown 
(fig. 63) densely covered with shoots. At the base of these 
shoots, roots are often formed. The aerial shoots are fre- 
quently rosette-like. The older light-shoots have a white, 
glossy cortex covered externally with long stiff protruding 
hairs. The ovate or ovate-elliptical leaves are also stifl- 
haired. The length of the leaves is 1—1,; (— 2) centimetres, 
the veins are very prominent on the lower surface and the 
depressions between them appear on the upper surface as 
convexities, so that the leaf has an embossed appearance. 
