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), formstlong 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 stiff- 

 haired. The length of the leaves is 1 1,5 ( 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. 



