THE DICOTYLEDONES 



182! 



into strands. Later, as a result of cell division of the parenchyma cells, 

 new cambial layers are produced in association with these strands and 

 form additional bundles of xylem and phloem. 



Apart from these anomalous stem structures, the morphology of the 

 leaf calls for special mention, though abnormalities do not occur in all 

 members of the family. The leaf may be either centric or bifacial and the 

 assimilatory tissue consists of one layer of palisade cells. In some forms 

 however the upper epidermis may be two or even three cells thick and from 

 the outer layer there may arise stellate hairs. The lower epidermis is often 

 papillose. The stomata often have a pair of subsidiary cells parallel to the 



pore. 



The genus Byrsonima is widely distributed in Central and South America. 

 It contains about 120 species, several of which are of economic importance. 

 B. spicata which occurs in the West Indies is known as the Shoemaker's 

 Bark; the bark of the tree being tanned and used in place of leather. 



The Zygophyllaceae are a small family of woody perennials containing 

 about twenty-two genera and 160 species. They are mostly tropical and 

 subtropical in distribution and live either under xerophytic or halophytic 

 conditions. The leaves are opposite, stipulate and usually hairy, fleshy or 

 leathery in structure. They form one of the chief components of the vegeta- 

 tion of the salt deserts. 



The anatomical features reflect the ecological habitat of the plants. 

 The leaves are often centric, with a central thin-walled water-storage 



Fig. 1728. — Guaiacum officimile. Shoot with flowers and a fruit. 

 (After Berg and Schmidt, fro»i Rendle.) 



