428 ARRANGEMENTS FOR RETAINING THE POSITION ASSUMED. 



leafy blades had been stroked like the hair of a horse's mane in the direction of 



the wind. 



The second arrangement for protecting broad flat leaves against crushing is 

 observed in fan-palms, in maples, poplars, birches, in pear and apple trees, and in 

 innumerable other woody growths of all regions. It consists in the development 

 of long, elastic leaf-stalks. The Aspen (Populus tremula), which may be regarded 

 as the best example, exhibits leaves on the branches of its crown, whose circular 

 blades are always somewhat shorter than the stalks. At the slightest movement of 

 the air these are seen to tremble and sway hither and thither, and this phenomenon 

 is so striking that it has furnished the nucleus of many sayings, such as to 

 "tremble like an Aspen leaf". But even in the most severe storms it is only 

 the leaf-stalks which bend, having acquired a high degree of elasticity by the 

 development of bast strands. The leaf-blades borne by them remain flatly ex- 

 tended, stiff, and rigid. They are not bent by the wind, and, therefore, these 

 elastic leaf -stalks ward off the danger of fracture from the blades they support. 



In many grasses for example, in the most widely-distributed cereals, wheat, 

 rye, and barley it is observed that the first green leaves developed by the 

 seedlings are erect, while those developed later, which arise from the slender 

 haulm which springs from their midst, are more or less parallel with the ground. 

 In many other plants with much contracted subterranean stem-structures, viz. 

 in the Reed-mace (Typha) and in many bulbous plants, all the foliage-leaves 

 assume an erect position and remain so until they fade and die. Leaves, when 

 erect, are far more exposed to the wind passing horizontally over the ground, and 

 require much stronger protections against bending than those which are extended 

 flatly over the soil; and in order that they may be able to escape fracture, they 

 must be provided with specially effective contrivances. 



The fistular leaf is to be regarded as one of the most striking of these 

 contrivances. Fistular leaves are always erect at the lower end, where they 

 surround the stem or the neighbouring leaves, like the equitant leaves of irises; 

 they are sheathing and hollow, terminating above in a hollow cone. There is no 

 conspicuous midrib; a shallow groove is frequently seen on the side directed 

 towards the central axis of the whole plant; otherwise the hollow leaf is developed 

 uniformly all round. It has no appearance of special resisting capacity, and those 

 cellular elements which, as a rule, are used to increase strength, are absent; and yet, 

 like all tubes, it possesses a relatively great resistance to flexion, and it is scarcely 

 injured, even in violent storms. On the whole, this striking form of leaf is not 

 common; it is most often seen in bulbous plants, e.g. in Chives and in the Common 

 and Winter Onions (Allium Schwnoprasum, Cepa, and fistulosum). Structures 

 are more often met with which resemble the fistular form to some extent, 

 since their long green blades are rolled up lengthwise, sometimes towards the 

 side facing the central axis of the whole plant, and sometimes away from it. 

 The rolling observed in leaves of crocuses is particularly noticeable. A white 

 central strip runs the whole length of the erect leaf, which is bordered by two 



