110 Transactions. — Botany. 



Art. VII.— r/ic Fall of the Leaf. 



By Joshua Rutland. 



Communicated by Professor Hutton. 



[Read before the Philosophical Institute of Canterbury, 6th September, 



1888.] 



Why deciduous trees prevail in the north temperate zone and 

 evergreens in the south is a question which can scarcely fail 

 to intrude itself on any one, however uninquiring, whose ex- 

 perience enables him to institute a comparison between the 

 forests of the two regions in their respective winter periods. 



To the emigrant from Britain, whose home is amidst the 

 wilds of the New Zealand bush, the contrast is most ap- 

 parent. Surrounding himself as he generally does with the 

 plants of his native country, he sees them unaltered in their 

 habit side by side with the indigenous productions, whilst he 

 is constantly reminded by the cold wdnter nights that the 

 climatic conditions of his old and new homes do not differ 

 very widely. Hence the reason why this difference is forced 

 upon and kept ever before him. 



The mere fact of northern species remaining unaltered 

 when removed to corresponding southern latitudes, and vice 

 versa, is sufficient to show that an answer to this question is 

 not to be found in the existing conditions of soil or climate, 

 while the exceptions that occur in both hemispheres prove 

 that the deciduous and non-deciduous habit cannot be entirely 

 due to the nature of the plants that constitute the respective 

 floras. 



For example : We have in Europe the guelder-rose {Vibur- 

 num opulus) and the laurustinus {Viburnum tiuus), belonging to 

 a purely northern genus, the former deciduous, the latter ever- 

 green ; and in New Zealand the ribbon-woods {Pla giant has 

 betulinus and P. divaricatus), evergreen or deciduous according 

 to the situation in w^hich they grow, the only other species of 

 this genus being Australian. 



As the fall of the leaf, which is the subject of this inquiry, 

 always takes place at the ajDproach of or during winter, we 

 are justified in concluding that a lowering temperature is the 

 immediate or most important cause of it. The problem we 

 have then before us is, why are not the effects more uniform ? 



For the examination of these effects there are probably 

 few places that offer such facilities as the Pelorus District, 

 wherein I now write. In the narrow bush- valleys and their 

 numerous branches, with encircling hills running into peaks of 

 3,000ft. elevation, and in the long, narrow, sheltered sound, 

 though extremely limited in extent, we meet with a variety of 



