Smith and Taylor: Note on the Lombardy Poplar. 233 



Black Poplar, it is well-marked. Since the influence 

 of the south-westerly winds is generally regarded as the 

 cause of these trees becoming permanently bent, it is in- 

 teresting to inquire why the Lombardy Poplar is almost erect, 

 w^hile some other poplars lean strongly to one side. 



Friih* points out that in a tree, whose crown has been 

 rendered asymimetric by the influence of a prevailing wind, the 

 twigs on the windward side are ' shorter, curved, often spinose, 

 and appear more or less blown in towards the crown, or are, 

 at least, poorly developed.' 



A well-marked feature of the Lombardy Poplar consists 

 in the twigs being curved in such a manner that their tips point 

 inwards towards the central axis of the tree. While this fact 

 is well-known, a more detailed examination shows that it is 

 not true of all the twigs of a given tree. It certainly holds 

 good for the twigs situated on three sides ; those, however, on 

 the fourth side, which is the side facing the south-west, do not 

 bend inwards but are straight or even bent outwards (fig. i).t 

 This peculiarity in the twigs may be illustrated by holding up 

 one's open hand, and gently flexing the fingers to represent 

 the curved twigs, and strongly extending them to represent 

 the straight ones. 



The difference in the behaviour of the twigs situated on the 

 south-west side, influences the symmetry of the tree as a whole : 

 there is only one plane along which it can be divided into two 

 similar halves. This plane is vertical, and lies in a south-west 

 and north-east direction. An observer viewing the tree from 

 either of these aspects, finds that the twigs on both sides curve 

 inwards towards the axis, and give to the general shape a fairly 

 symmetrical appearance (plate xxiii.). If, however, he views the 

 tree from a direction at right angles to this plane, that is from 

 either the south-east or the north-west, he will notice that the 

 twigs on one side are curved as before, while those on the other 

 side are straight, or nearly so, and that, in consequence of this 

 difference, the appearance of the tree is rendered asymmetric 

 (plate xxiv.). 



The Lombardy Poplar exhibits a further feature of interest. 

 The tips of the leading branches situated at the summit of 



* T. Fruh : Die Abbildung der vorherrschenden Winde durch die 

 Pflanzenwelt. — Jahr. Geo-Ethn. Geo. Zurich, 1901 -2. 



t The photographs from which the illustrations are taken, were 

 obtained during March and April of the present year. 



J908 July I. 



