THE QUEST FOR LIGHT 281 



bristles, by which the plant clings to supports. It is an 

 exceedingly common denizen of hedgerows, and a most 

 vigorous scrambler. It should be remarked that a 

 peculiar plant device may possibly serve more than one 

 purpose. The hooks of the Bramble, for example, not 

 only ensure a place in the sun for the leaves, but also a 

 conspicuous display of the flowers and fruit. This dis- 

 play has relation to insect pollination and the scattering 

 of seeds by the agency of birds. 



Mention must also be made of the twining plants, 

 which twine round other plants, and thus use them as 

 supports in their lightward progress. Members of the 

 Convolvulus family are familiar examples, as also are 

 the Hop (Humulus Iwpulus), the Honeysuckle (Lonicera), 

 and the Black Bryony {Tamus communis). The Hop 

 produces T-shaped hairs, which are quite stiff, and 

 evidently assist in making good the progress of this 

 twiner. 



Other plants have developed tendrils which during 

 their growth are very sensitive to contact, and when 

 they come into touch with a support, they rapidly twine 

 around it. Thus, stems which are too weak to support 

 themselves in an upright position are able to be drawn 

 upwards to light and air. The tendrils may be modified 

 leaves, stem structures, or roots. In the Vine they are 

 modified floral branches, as is also the case in the Pas- 

 sion Flower (Passiflora). In the Vetches (Vicia, Plate 

 XLIX.) and the Peas (Lathyrus) the terminal leaflets are 

 replaced by tendrils, and in their case the tendrils may 

 be regarded as modified leaflets. The Clematis grasps a 

 support by means of its leaf-stalks (petioles) , which are 

 very sensitive to contact, and twine round a support 



36 



