412 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



character of Thuyas, our own Ling, New Zealand Alpine species of 

 Veronica, &c, as well as in saline plants, as our Saltwort, and in some 

 desert plants (e.g. Salsola Pachoi, of Egypt). This identity of leaf- 

 form arises from a similar response to drought in all these different 

 localities ; but in the case of plants in salt-marshes, though moisture may 

 be abundant, it is not so serviceable as if devoid of salts. Consequently,, 

 saline plants are said to be 1 ' physiologically xerophy tic." Even Man- 

 groves, which may actually grow below high-water mark, are xerophytic 

 in their structure. The methods of securing and retaining a sufficient 

 amount of water among epiphytes are various. Thus Orchids and Aroids 

 are provided with similar absorbing roots, the outer coat, called the- 

 velamen, being capable of absorbing water as easily as blotting-paper. 

 Tillandsia usneoides has its stems provided with colourless scales which 

 absorb water. Other Bromeliads form water-tanks by the close imbrica- 

 tion of. their leaves, so that they assume the form of a shuttlecock- 

 Orchids have water-storage tissues in their pseudo-bulbs, &c. The great 

 Banyan trees of India (Ficics indica) begin life as epiphytes, but they 

 soon send down roots which penetrate the soil. Having killed the original 

 host-trees, they finally grow into the well-known gigantic form supported 

 by myriads of vertical root -props. 



Lianes. — These are woody-stemmed climbing plants, and are of great 

 variety. Their methods of climbing differ in several ways ; thus, some 

 climb by means of tendrils, others by clasping roots, others by means of 

 hooks, just as we have herbaceous plants climbing by like methods in 

 England, the Honeysuckle and Clematis being our only woody-stemmed 

 climbers. The structure of the stems is usually anomalous ; the preva- 

 lence of much corky matter or large medullary rays adds much elasticity 

 to them, the wood being accompanied by large vessels which can convey 

 fluids rapidly to great distances, for they often extend to some hundreds 

 of feet in length, as do the climbing Palms or "rattan canes." A promi- 

 nent feature in the structure of the stems of Lianes is the methods adopted 

 to secure great strength coupled with elasticity — a combination of features 

 often aimed at by engineers and secured in much the same way. Thus 

 in some stems supernumerary small ones form outgrowths along the- 

 main axis, which, by becoming twisted, exactly resembles a cable. In 

 some (Banhinia) the stem is a flat ribbon at first, but soon bulges into 

 cup-like depressions on alternate sides, the whole having a corrugated 1 

 appearance. Very similar corrugations are made in boilers to resist the 

 pressure of the steam and to allow of expansion. Sheet iron is also 

 corrugated so as to impart additional strength. Similarly, the spokes of 

 certain wheels are curved like an S. This is to allow for tension on 

 cooling, so that they may not be torn away from the rim, as the rates of 

 cooling are different. The ribbon-like stems of Bauhinia are sometimes- 

 made stronger still by means of flanges down the edges. 



The above are illustrations of adaptations acquired in response to- 

 mechanical strains, as soon as they are felt by the plant. The actual 

 fine and slender tendrils by which some Lianes climb add additional means 

 of security, being often coiled up so as to allow considerable play against 

 being torn away from the support. There may be many coils, but, in 

 order to avoid breaking, some turn one way and others the reverse. This 



