60 
FLOBA OF ADEN . 
writes Anderson, “ the development has not attained actual spinosity, 
still in rigid or distorted branches and asperities of stem aud leaf bears 
witness to the modifying influence of the climate. Of the ninety-four 
species [of Anderson] 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 europeeum and Euphorbia, cuneata the 
short stiff branches are terminated by short thorns."” Of the many 
species which show one or the other of these modifications we mention ; 
Capparis galeata , Fagonia cretica , Zizyphus lotus , Z. spina Christi , 
Spheerocoma, Hooheri , Acacia Edgeworthii , A. eburnea , A . hamulosa , 
A. spirocarpa, A. nubica , Bleharis edulis , Jatropha spinosa , Alhagi 
maurorum. 
“ Several species yield gums or resinous matter, and their stems fre- 
quently become encrusted by these exudations, probably caused by the 
bark cracking from the exposure to the great heat of the sun. I have 
observed resinous substances accu nulafced in various quantities on 
Balsamodendron opobalsamum , Acacia Fdgeworthii , Adenium obesum, 
and the shrubby Euphorbia. All the Capparidacea , [of Anderson] 
(with the exception of Mcerua Thomsoni), Bipterygium glaucum, 
Reseda amblyocarpa , the Composites and a few others, are characterized 
by more or less pungency or aromatic odour, — qualities always possessed 
by plants of desert regions."” 1 
4, Flowering Season and Climate. 
We give in the following diagram the relative values of temperature, 
rainfall, flowering and fruiting season during one year, beginning with 
April. Unfortunately no observations on humidity were available, 
though it is just humidity which plays an important part in the regula- 
tion of the processes of reproduction 2 ). 
The curve of temperature gives the average of the mean monthly 
temperature from April 1878 till March 1876 as observed in the Camp, 
whilst that of rainfall shows the average of the monthly rainfall 
from April 1872 till March 1876. 
With regard to the flowering and fruiting season it is well to bear in 
mind that the data which form the basis of our curves stretch over a 
period of 60 years. The drawbacks of comparing values of different 
periods are evident. 
1 Anderson, 1. e. p. VIII. 
2 For a fuller account of these relations see our paper on <f Flowering Season and 
Climate,” in Journ, Bomb. Nat. Hist. Soc., Vol 17, p. 334-350, 697-708. 
