112 JOI RXAL OF THE KOYAL HORTICULTURAL SOCIETY. 



PKCriJAIUTIES OF THE CAPE FLORA. 

 By Rev. Professor G. Henslow, M.A., V.M.H., &0. 



Introductory Observations. — The general facics of the flora of a 

 country with a relatively dry soil and atmosphere, as that which prevails 



\in South Africa, and especially the western half, is very observable ; and 

 when it is found to be the same in varying degrees in widely separated 

 countries, as in the deserts of North Africa, in the arid districts of India 



.and Thibet, of Afghanistan, in parts of Australia, Brazil, Mexico, &c, so 

 that these several countries afford very similar appearances in their re- 

 spective floras, one infers (but of course, at first, merely on a priori 

 grounds) that most probably similar causes have produced these similar 



•results. A closer inspection shows that the similarities in the vegetative 

 systems of plants, which often have no affinity between them whatever, 

 can be carried down into the minutest details of histological structures. 

 Moreover, a large proportion of such structures at least are always service- 

 able to the plants in resisting the deteriorating effects of an insufficient 

 supply of water, as well as of an excess of radiation and other hindrances 

 to such vigorous growth as is maintained in moister climates. 



We thus begin to suspect, indeed very strongly, that the various 

 peculiarities obtaining are the direct results of the dry climatal conditions 

 Burrounding the plants, and that the unfavourable environment actually 

 brings about the production of just those kinds of structure which are best 

 able to resist the injurious effects of the climate, and so enables the plant 

 to survive under them.* 



The country north of the Cape — omitting the eastern half — is 

 characterised by a very dry climate, the rainfall being under 10 inches 

 per annum; and it is to this great absence of water that the flora is 

 particularly specialised. 



With regard to the rainfall in South Africa there is a marked difference 

 between the east and west sides. In the former there are two maxima 

 of 3'5 inches, in February and March, and again in November, the mini' 

 mum being i-25 inch in June, such being the average of twenty-two 

 years at Graham's Town. 



On the oilier hand, there is only one maximum, of about 4-5 inches in 

 Tune, taken at the Observatory, near Cape Town, being the average for 

 forty-two years. The minimum is about half an inch for each month of 

 the summer, viz. December, January, and February. 



The mean temperature of January at Cape Town is 70° F., while it 



•rises to 80° P. in the interior, as at Kimberley. In July it is 58° at the 

 former and 62° at the latter. 



The first point to remember is that plant life cannot exist without 



* Cntroduotion to "The Origin ot Plant Structures by Self-adaptation to the Environ- 

 ment exemplified bj De ert or Xerophiloua Plants." Journ. Linn. Soc, Botany, xxx. 

 L898, p. 21b. 



