18 



KNOWLEDGE. 



[January, 1903. 



specialized climbers. Climbing is a device resorted to by 

 many of our native plants, and by a far larger number in 

 the Tropics, by which, iu the keen struggle for light and 

 ail', thev take advantage of t.heir neighbours to mount on 



Fig. 1.— " Kuockin' Whiiis " for Cattle, Co. Antrim. 



TE. Welch, Photo. 



their shoulders, and thus secure an advantageous position. 

 To assist them iu climbing, plants adopt various devices, 

 some merely scramble upwards, maintaining their position 

 by means of wide-spreading leaves or branches ; many 

 others use downward-pointing hooks, which anchor them 

 amid the foliage. It is in the twining plants, such as 

 Bryony and Hop, aad the tendril-beai-ers, like the Vetches, 

 that we find the highest development of the climbing 

 habit. These plants live under unusual conditions. In 

 order to gain the light, they must seek, rather than avoid, 

 overhanging foliage ; and so we find the Vetches, instead 

 of turning away from the shadow towards the light like 

 most of their neighbours, boldly pushing up into the 

 centre of a bush, to burst into blossom amid its upper 

 branches, far above their less daring neighbours. Again, 

 in these plants, supported by their grasp of adjoining 

 branches, the stem no longer needs to act as a supporting 

 column, bearing the weight of the plant aud the stress of 

 weather. It acts rather as a conduit through which water 

 and dissolved salts — the raw plaut-food — passes upwards 

 to the leaves. Hence, instead of being thick and stiff, it 

 is thin and flexible; often wonderfully slender when we 

 consider its length, yet strong and supple, to follow without 

 injury the swaying of the supporting plant. But it is in 

 the leaves of these plants that we find the most remarkable 

 modifications adapting them to a climbing habit. The 

 leaves of the Vetches and Vetchlings are ]iinnate — they 

 bear a number of opposite ovate leaflets. The tip of the 

 leaf- stalk, and the uppermost pair of pinn«. are in the 

 climbing species changed into tendrils — sensitive, twining, 

 whiji-like structures, which exhibit remarkable features. 

 If the slightly curved, extended tendril of a young leaf of 

 Pea or Vetch be watched carefully, it will be found that 

 it is slowly but incessantly moving rouud and round iu a 

 cii-cle. If the tendril comes into contact with a twig, it 

 bends towards it, and eventually takes several turos round 

 it. Even a slight temporary irritation is sufficient to 

 cause a bending towards any side. Finally the tendril 



.^ 



i^ 



Fitt. 2.— Leaf of 

 Bush Tetcli, Viciu 

 sepiuiii. Half natural 

 size. 



becomes woody aud strong, and forms 

 a secure anchor-cable for the plant 

 Not only does the young tendril rotatr : 

 the whol(> leaf on which it is borne is iu 

 continual motion. The shoot to which 

 the leaf belongs is rotating also, so that 

 the tendril is sweejjing the air with a 

 complicated motion, in the course of 

 which it is almost sure to strike against 

 some stem or twig of the surrounding 

 vegetation. It is interesting to note 

 that a few species of these climbing 

 genera are low- growing, make no 

 attem|it to climb, and that in these, 

 tendrils are not developed. Such are 

 the Wood Bitter Vetch (Vicia Orobus), 

 which grows in bushy clumps, and the 

 tiny Spring Vetch (V. lathyroides), 

 whose home is on short sandy turf. 

 Also the well-known Tuberous Bitter 

 Vetch {Lathijrus macrorrhizus), and the Black Bitter 

 \'etch (L. niger). In all these the stem terminates 

 neither in a tendril nor iu a leaflet, but in a short 

 point. Two other native species of Latliijrus possess 

 pecidiar leaf-modifications which are woithy of study. In 

 the Grrass-leaved Vetchling {L. NissoUa) no leaflets are 

 ]3roduced, and instead the leaf-stem which usually bears 

 them is expanded into a narrow flat leaf, which so nearly 

 resembles those of the grasses among which it grows that 

 it is almost impossible to detect the plant when it is not 

 in flower. The seed-pods also are long, narrow, and green, 

 and only the solitary rose-red blossoms betray the presence 

 of the plant. The Yellow Vetchling (L. Aphaca) has gone 

 to another extreme. Its leaf is wholly converted into a 

 long undivided tendril. To act as a substitute in the 

 important work of assimilation, the stipules, which in the 

 Vetchlings usually take the form of a pair of small leaf- 

 like organs clasping the stem at the base of each leaf-stalk, 

 are here enlarged, and form a pair of large triangular 

 pseudo-leaves at each node. From the axil of the tendril - 

 leaf springs the flower-stalk, bear- 

 ing a single yeUow blossom. To 

 convince ourselves of this curious 

 shifting of responsibility we have 

 ouly to examine seedlings of the 

 plant. We then find that just as 

 the seedling Gorse shows true 

 tiifoliate leaves giving way to 

 spines, so in this species the first 

 leaf has a pair of leaflets, and is 

 accompanied by a pair of stipules 

 of the normal size and shape. 



The familiar peculiarly shaped 

 flower of, for iustsince, the Sweet- 

 Pea, Broom, or Laburnum, is most 



characteristic of the sub-Order Papiiionaceas, to which 

 belong all our British Leguminonie. This flower is 

 profoundly modified to suit the visits of insects, which 

 effect cross-fertilization. The axis of the flower, as iu 

 most of the more highly specialized entomophilous flowers, 

 is horizontal. The calyx is more or less cup-shaped, 

 with five teeth of varying length, and it is persistent 

 throughout the period of flowering and fruiting. The 

 corolla consists of five jjctals. The upjier oue (the 

 stiitiJurd) is large aud broad, often variegated with 

 stripes of a second coloiu-, aud forms a kiud of roof. 

 Two narrower ones (the icings) are placed below, oue on 

 each side ; and more or less enclosed by them, the fourth 

 and fifth are slightly joined together along their lower 

 margin, aud form the keel. Ten stamens spring, like the 



Fig. 3. -One Node 

 of Yellow Vetchling 

 {Lafht/rus Aj'haca.) Half 

 natural size. 



