205 



rule they do not exceed 30 centimetres. They have a white 

 bark, and are usually branched, branch-thorns arising in the 

 leaf-axils; the leaf-base is thick and persistent. The branch- 

 thorns are generally short, about 1 centimetre long, and often 

 bear only two leaves placed low down near the base. The 

 branch-thorns may, however, become longer and bear several 

 pairs of leaves. The flowers arise from the base of the 

 branch-thorns either in the axils of the two low-set leaves, 

 or next year they form part of the rosette-shoots which appear 

 in the axils of these leaves. On 

 long branch-thorns the flowers may 

 also arise higher up. 



The year-shoots generally ter- 

 minate in a thorn; their distal part 

 always seems to die away. 



They flower during summer. 



The leaf is isolateral in struc- 

 ture. There are stomata on both 

 sides, generally flush with the sur- 

 face but some of them are slightly 

 raised and below them is a group 

 of cells, 2 4 on each side, which 

 are round and devoid of chloro- 

 phyll; throughout the rest of the 

 leaf these cells are wanting (fig. 45). 

 The palisade tissue is 2 3 cells 

 thick, and towards the interior it merges gradually into a 

 large-celled aqueous tissue containing a slight amount of 

 chlorophyll. The veins which lie a little nearer the upper 

 side than the lower, have bundles of bast on both sides and 

 here are found a few perfectly translucent cells. 



Fig. 45. Lijcium ruthenicum. 

 Part of leaf in transverse sec- 

 tion. X 203. 



Nitraria Schoberi L. 



A shrub, barely one metre high which prefers the clay- 

 desert. The bark is white, the leaves are thick and spath- 

 ulate with short hairs, and are placed 24 together on a 

 small cushion, with small scales between them. The leaves 



