702 CLIMBING PLANTS. 



much more likelj'^ to break off at the base than the united surfaces to separate when 

 the roots are forcibly displaced. 



The following types of climbing roots may be distinguished according to their 

 shapes. First densely crowded, simply or only shortly branched, filamentous roots, 

 arising in groups, but each separately from the stem; these are increased in 

 number by the production of new batches as the lignifying stem becomes older 

 and thicker, and they sometimes grow together and border the stem, adhering to 

 the substratum in irregular, membrane-like rows. On older stems the climbing 

 roots are usually for the most part dried up, and those which have not united with 

 the support then project from the sides, often forming shaggy beards, and giving a 

 very odd appearance to the stem. The Ivy (Hedera Helix, of which old stems are 

 shown growing up on an oak in fig. 167) may be taken as an example of this type. 



The second form presents a wholly different aspect; as the type we may select 

 the Tecoma radicans, a native of the southern United States, often used for 

 covering garden -walls. The climbing roots here are strictly localized. At each 

 node of the shoot below the point of insertion of the leaves a paired cushion-like 

 structure arises, and from each of these cushions several rows of protuberances, 

 which grow out into as many rows of unbranched or shortly -branched, fringing 

 fibres, 1-5 cm. long (see fig. on p. 479). The epidermal cells of this fringe, which 

 come into contact with a firm substratum, elongate and form root -hairs, that is, 

 papilliB and tubes, which in a veiy short time fasten to the support; after this thej- 

 turn brown and die, thus never functioning as absorbent organs. 



A form materially differing from these is shown by the climbing roots of the 

 cactus Cereus nycticalus, known as the "Queen of the Night", which is repre- 

 sented in Plate VII. (facing p. 641), and also of several tropical BigTioniaceaj, and 

 especially in Ficus stipidata, so often used in greenhouses for covering the walls. 

 In the last-named plant the climbing roots arise in fascicles in the shade of the 

 green leaves; they are filamentous and terminate in many hair-like, spreading 

 rootlets. They adhere by root-hairs to the substratum, and thus fasten to it the 

 tender, pliant stems. These roots are not very long and soon dry up, but close 

 behind them much stronger roots arise from the stem, which has meanwhile become 

 thicker, and these traverse the walls like cords, repeatedly branching and intersect- 

 ing, and form actual net-works, often becoming several metres long. These latter 

 roots do not help much in fastening the stem to the supporting wall; they are 

 absorbent roots, and take up the atmospheric water, with its abundance of food 

 materials, which has condensed or trickled down the bark of trees and rock walls. 



The clasping roots borne by the stems of Wightia, a genus of Scrophulariaceaj 

 growing in the mountainous regions of the Himalayas, and of several species of 

 fig in the same district, may be regarded as a fourth type. The attachment of the 

 young shoots is brought about here as in the form just described by the finely- 

 branched but not much elongated roots, which soon dry up. But when the climbing 

 stem begins to thicken much stronger roots arise which surround the supporting 

 tree-trunk like clamps and actually engirdle it. These girdle-like clasping roots 



