Cockayne. — Plant Geography of the Waimahanri. Ill 



the plain is a clear blue sky, while a hot sun strikes down. 

 On plants the leaves hang flaccid, in orchards the trees are 

 stripped of their fruit ; everywhere the surface of the ground 

 becomes dry as dust. On the dunes clouds of sand are blown 

 back to~ the sea, sandhills are bodily removed, and the rope- 

 like stems, several metres in length, of Desmoschcenus laid bare. 

 In openings in the mountains, such as Porter's Pass, the fury 

 of the storm is something to encounter. Mr. J. Rountree, for 

 many years driver of the West Coast mail-coach, tells me that 

 the coach is sometimes forced to halt near the summit of the 

 pass, unable to proceed except with great risk of being over- 

 turned, and that small stones are meanwhile carried witli 

 great force through the air. When the north-west wind rages 

 on the mountains, it is frequently impossible to stand upright 

 on a ridge exposed to its full blast. Where such a wind 

 blows even heavy seeds need no special provision for their 

 distribution. 



Fifthly, as to Radiation.— Hector writes {I.e., p. 429), 

 " The effect of the prevalence of clouded sky is best illustrated 

 by the average difference between the readings of the black- 

 bulb maximum thermometer in the sun and of the minimum 

 thermometer exposed to the night-sky, and for this purpose 

 two stations on either side of the Southern Alps may be 

 selected : — 



Christchurch. 



Insulation. 



Radiation. 



Hokitika. 



Difference., Insulation. Radiation. 



Differ- 

 ence. 



Summer 

 Autumn 

 Winter . . 

 Spring . . 

 Extremes 



35-64 

 31-32 



28-26 

 35-46 

 75-42 



Acclimatisation. 



The behaviour of introduced exotic plants with regard to 

 hardiness, rapidity of growth, variation in form both externally 

 and internally, or of change with regard to reproduction and 

 the like under their changed climatic conditions, is of great 

 value for furnishing details regarding climate. Information of 

 this kind would be an interesting contribution to plant geo- 

 graphy in general, and the subject is well worthy of extended 

 treatment. Here I can only deal most briefly with this 

 matter, confining my remarks for the most part to the ques- 

 tion of hardiness, and selecting first of all a few common 

 plants. 



