189 



branches are arranged in bunches (A. Ammodendron, hyrcanus 

 and perhaps others). 



My knowledge of these Astragalus-species is mainly 

 derived from literature and herbarium material. 



Fig. 35. Halimodendron argen- 



F, Wood; Phi, Phloeum; C. Cork. 



belongs to a leaf-rachis thorn, 



the next largest to a stipular 



thorn. X 24. 



Halimodendron argenteum D. C. 



A shrub attaining a height of about 2 metres, which 

 prefers clayey soil. It is also common in the neighbourhood 

 of rivers and is often met with in oases, by roadsides and 

 such places. It has long, hori- 

 zontal roots from which aerial 

 shoots issue at long intervals. 



The year -shoot seems to 

 become completely lignified and 

 to remain alive throughout its 

 whole length. The primary 

 bark is green, the secondary 

 brown. Within the bark and 

 surrounding the branch there is 

 a circle of six large bast-bundles 

 (fig. 35), three larger ones on 

 one side corresponding to the 



nearest leaf above with its two stipules, and three smaller 

 ones on the other side corresponding to the next but one 

 set of leaves higher up. All the bundles disappear at a 

 distance about I 1 /* nodes below the leaf from which they 

 issue. The lower part of each node of the stem has there- 

 fore only three bast-bundles. The rachis of the leaf and the 

 stipules form thorns, and the larger bundles of sclerenchyma 

 in the bark are the downward prolongations of the thorns. 

 The intervening spaces are not quite regular as the leaf-arran- 

 gement is a 2 /?> spiral. The structure of the bark (and the 

 pith) has been described by B. JONSSON (p. 31) who has 

 found mucilage-cork and air-lacunae; I have not examined 

 these. JONSSON calls the persistent leaf-rachis a thorn-branch 

 bearing leaves arranged in pairs and accompanied by second- 

 ary thorns. The real condition is that the leaves are pinnate 

 with four cuneate leaflets. The rachis remains as a thorn 



