58 
FLOBA OF ADEN. 
Amongst the many contrivances for regulating the water-supply, 
the most efficient protection from too great a loss of water by transpira- 
tion is obtained by the reduction of the evaporating surface. Of the 
numerous plants which have their leaves reduced in size, and sometimes 
also in number, we mention : Farsetia longisiiiqna , Cocculus cebatha , 
Dipterygium glaucum , Cleome papillosa , Cleome hr achy car pa, Cl. para- 
doxa, Mama T/iomsoni, Cadaba glandulosa, Polygala 1 erioptera , Poly - 
carpaa corymbosa, Spharocoma Hooheri, Corchorus antichorus, Greivia 
populifolia, Zygophyllum simplex, Commiphora opobalsamum , Moringa 
aptera, Indigofer a semitrijuga, I. arabica , I. paucifolia, I. parvula, 
Tavernier a glauca, Ehynchosia minima , Oldenlandia Schimperi, Helio - 
tropium strigosum, Convolvulus glomeratus, Linaria macilenta, Schwein- 
furthia pterosperma, Campylanthus junceus, Lavandula setifera, Saltia 
papposa, Suada fruticosa, S , vermiculata , Euphorbia arabica, F. cuneata, 
E. systyla, Ephedra foli at a. 
The leaves of many plants are quite normal as regards size and 
shape, in which case various structural modifications bring about the 
necessary decrease in transpiration. 
A very common modification is the cutinized leaf, in which the outer 
wall of the epidermis is thickened and rendered impervious by the addi- 
tion of cutin. The cuticle, filling sometimes half or more of the cell 
cavity, is usually thicker upon the upper surface of horizontal leaves ; 
upon upright or oblique ones it is more uniformly developed. The texture 
of cutinized leaves is usually leathery. Practically most Aden-plants 
with smooth leaves of the normal form belong to this type. 
Another modification, well represented in Aden, is the lanate leaf. 
It is distinguished by dense hairy coverings upon one or both surfaces. 
The hairs may be short, long, repeatedly branched or curved, and even 
glandular. Where there is a dense layer of hairs, the epidermis is usually 
not provided with a cuticle. The function of the hairs is to decrease 
transpiration by protecting the epidermis ; the amount of light and heat 
is diminished and the access and movement of dry air impeded. It 
is evident that a few scattered hairs are of little or no value for this 
purpose. Examples of this type are : Farsetia longisiliqua , Eiplotaxis 
pendula, Polygala erioptera, P. Thurmanniana Pvlycarpaa fragilis, 
Melhania Eenhamii, Iribulus terrestris , etc. 
A third modification is the so called storage-leaf, containing water 
storage cells in the chlorenchyma. Their function is to increase the 
water supply by storing the surplus of absorbed water against a time of 
need. Examples : Maerua crassifolia, Zygophyllum simplex, Portulaca 
quadrifida , Spharocoma HooM'i . 
