Vlll FLOBTTLA ADENENSIS. 



the globe, is quite unknown at Aden. Here foliage is reduced to 

 a minimum, and the superfluous moisture given off by leaves in less 

 arid climates is stored up in fleshy stems against seasons of long- 

 continued drought. "With the exception of some Capparidacece 

 and Reseda amblyocarpa, all the plants have either glaucous 

 whitened stems and leaves, or are completely covered with a hoary 

 pubescence. 



Aridity, while reducing the amount of cellular tissue, has also 

 favoured the production of spines; and though in many cases 

 the development has not attained actual spinosity, still in rigid 

 or distorted branches and asperities of stem and leaf bears witness 

 to the modifying influence of the climate. Of the ninety-four 

 species that constitute the flora, sixteen bear sharp thorns on some 

 part of their structure. In some the leaves terminate in sharp, 

 recurved hooks ; in others the stipules are spinous ; in a few the 

 bracts are prickly, and in Lycium europceum and Euphorbia cuneata, 

 the short stiff branches are terminated by short thorns. Several 

 species yield gums or resinous matter, and their stems frequently 

 become encrusted by these exudations, probably caused by the 

 bark cracking from exposure to the great heat of the sun. I have 

 observed resinous substances accumulated in various quantities on 

 Balsamodendron opabolsamum, Acacia JEdgeworthii, Adenium obeswm, 

 and the shrubby EupJiorbice. All the Capparidacece (with the 

 exception of Mcerua Thomsoni), Dipterygium glaucum, Reseda am- 

 blyocarpa, the Composites, and a few others, are characterized by 

 more or less pungency or aromatic odour, — qualities always pos- 

 sessed by plants of desert regions. 



The small proportion of species to the number of genera and 

 Natural Orders will be perceived by an examination of the accom- 

 panying Table : — 



Genera. Species. 



Cruciferae 3 3 



Capparidaceae 4 9 



Resedaceae 1 1 



Polygalacese 1 1 



Caryophyllaceae • • • • 2 2 



Malvaceae 2 3 



Sterculiaceae 1 1 



Tiliaceaj 2 2 



Geraniaceae 1 1 



Zygophyllaceae .... 2 2 



Rhamnaceac 1 1 



Terebinthacea3 .... 1 1 



Genera. Species. 



Moringeae 1 1 



Leguminosae 8 11 



Cucurbitaceae 2 2 



Portulacaceae 2 2 



Umbelliferae 1 1 



Rubiaceae 1 1 



Composite 5 5 



Apocyneae 1 1 



Asclepiadaceae 2 2 



Convolvulaceae 2 3 



Boragineae 1 1 



Solanaceae 1 1 



