114 Transactions, — Botany. 



We cannot from observation explain the formation of 

 alpine floras, but wherever they exist we see that they 

 correspond in their general aspect with the flora of the 

 surrounding region. Thus, the mountains of Australia and 

 Tasmania are clothed with plants essentially Australian, 

 evergreen trees ascending to the limits of arboreal vegetation. 



In like manner, typical New Zealand species — such as 

 Veronicas, Coprosmas, and Pittosporums — are found in our 

 alpine heights. Nor do the few deciduous trees we possess 

 particularly affect those elevated regions. One only seems to 

 owe its deciduous habit to the alpine cold, Placjianthus lyalli, 

 which the late Sir J. Haast observed as " a deciduous tree at 

 and above 3,000ft., but evergreen below that line." 



The two allied species, PlagiantJms betidinus and P, 

 divaricata, both deciduous, belong to the lowland country ; the 

 former, in this district, invariably growing on the low rich 

 land of the inland valleys, the latter fringing the tideway 

 throughout the sound. A careful scrutiny of the flora of any 

 extensive and varied region will at once reveal the fact that 

 the horizontal and vertical range of species do not always 

 coincide, for it is not the plants of the highest latitude which 

 are invariably found closest to the summits of high mountains. 

 The reason of this becomes apparent when we examine the 

 distribution of the plants within any limited mountainous dis- 

 trict traversed by deep valleys, bearing in mind as we do 

 so what has been so clearly pointed out by Liebig in his 

 " Natural Laws of Husbandry " — viz., that " all plants which 

 give landscapes their peculiar character, clothing the plains 

 and mountain-slopes with perennial green, have an under- 

 ground development, according to the geological or physical 

 condition of the soil, admiralDly adapted to their perennial 

 existence and propagation." In this district, for example, we 

 have two very distinct classes of land, the low alluvial flats of 

 the valleys, and the steep hill-sides, with an intermediate class 

 consisting of level terraces, composed of rock - fragments 

 imbedded in gravel and clay. 



Now, in the alluvial flats and hill-sides respectively we 

 find certain species of plants which never encroach on each 

 other's territory, though most of them intermingle on the 

 terrace lands. Amongst those which most strictly adhere to 

 their proper habitat are the deciduous Plagianthtis hetulimis 

 and P. divaricata before mentioned. As both species range to 

 the southern portion of the island we are forced to conclude 

 that it is not inability to withstand cold, but an inability to 

 adapt themselves to any other than the deep soil in which 

 they invariably grow, that determines their vertical range. 



It can thus be seen how, in the process of selection which 

 must take place through the elevation of a portion of ai 



