110 BOTANY. [CHAP. in. 



superseded the old-fashioned woody trunk. The long, slen- 

 der, weak-stemmed climbing and twining plants illustrate 

 the later method. As British examples, we may mention 

 the ivy, honeysuckle, convolvulus, etc. ; amongst exotic 

 plants, the vines, and those numerous forms that stretch 

 from tree to tree in tropical forests. Our roses and 

 brambles illustrate an incipient attempt in this direction, 

 their spines, that were in all probability protective 

 against animals, becoming in many species curved down- 

 wards, and serving as anchors that hook on to neigh- 

 bouring plants, and thus become elevated to a certain 

 extent at the cost of the neighbour. The method by 

 which the ivy clings to its support has been already 

 explained. Coming to such plants as the hop, where 

 the stem twines round a suitable support, we encounter a 

 higher stage of development due to the influence of 

 light, or rather to the more highly organized protoplasm 

 being enabled to utilize light to a greater extent than 

 plants lower down in the scale of life. The highest 

 stage of development reached by plants that have 

 adopted the long slender stem is illustrated by the grape- 

 vine and most of the peas and vetches. In such plants 

 the stem does not coil round a support, but is firmly 

 anchored by numerous slender threads known as tendrils 

 that become firmly coiled round the slender branches of 

 other trees. These tendrils are not new special parts 

 developed for this purpose in addition to the parts pre- 

 viously possessed by such plants, but are old parts 

 modified to serve this special purpose. The tendrils of 

 the vine are modified flower-stalks, those of the peas and 

 vetches in like manner are portions of the leaves. 

 Tendrils differ from twining stems in not coiling up 



