386 EFFECTS OF DRdUCHTS ON niSf'KI III'TION OF PLANTS. 



III. The Impo\'ekishment of the Flora of a Locality and 

 OF A Whole District through Climatic Conditions, 

 vie.. A Severe Drought. 



The indigenous vegetation of tlie Cape Peninsula as well as 

 the introduced plants principally depend for the necessary water 

 upon the winter rains, as the following table will sliow : — 



Rainfall at the Royal Obscn'ato'y, near Capetown. 

 The means {iiiehes} ealeulated from a period of 22 years. 



Jan. Feb. March. April. A [ay. June. July. 

 0.82 0.59 1. 10 2.16 4.17 4.05 4.12 



Aug. Sept. Oct. Nov. Dec. Year. Alin. 

 3 . 54 2 . 48 I . 85 I . 06 o . 86 26 . 80 20 . o 



Rainfall for the Summer Months (nieani. 



Four months' 

 Three months F(Hir months Minimnm for 



(Dec. Jan., Feb.) ( Dec. -March ) period of 60 years. 



'2.27 3.37 0.79' 



(,1950/51) 



It will be seen that while the four winter months ( May- 

 August ) bring 15.88 inches of rain, the four summer months 

 (December-March) show only ^.^y. riie real significance of 

 this figure is, however, not apparent imless one examines the 

 individual years from which the mean has been deduced, for 

 while the minimum for the whole year is 20 inches — i.e., 74. f> 

 per cent, of the mean — the minimum for the four summer months 

 during the last 25 years is T.27 — i.e., 2)7 -7 pei" cent, only, and 

 in some neighbouring districts, vi:~., Wellington and Piquetberg, 

 it sometimes happens that no rain whatever falls during this 

 period. 



These are the years which decide the fate of many a plant 

 which may have spread beyond the former boundary of the 

 species, the fate of many a foreign tree, which may have grown 

 to a considerable size during tlie years with an average or spe- 

 cially-favoured summer. 



The sumiuer of 1914, 15 v.-as such an extreme season, for 

 not only the meteorological records, but also the effects pro- 

 duced, show it to have been so. 



In the neighbourhood of Capetown one may see a good many 

 full-grown trees of various kinds which died during this season, 

 viz., Aurac aria (Norfolk pine ), Cnpressus maeroearpa (cypress), 

 Sehinus mofle (the pepper tree), lin.ealyptns ficifolia (the red 

 flowering gum), and various other eucalypts, among them also 

 the usually drought-resisting Eucalyptus globu'liis (blue gum). 

 ( )f the latter species some fairly large trees, probably 50 years 



