700 CLIMBING PLANTS. 



and crannies of stone or bark and actually creep into them, or when only shallow 

 grooves are to be found in the substratum, bur}^ themselves in them. Smooth 

 surfaces are avoided as far as possible since they afford no suitable hold to this class 

 of tendril. When established in the chinks and crevices, the ends, vsrhich until now 

 have been hooked, swell out like a club or ball, and in a short time thicken so much 

 that they occupy the entire crack. It looks as if melted was had been poured into 

 the crevice and had then solidified and fitted itself to all its inequalities. The 

 growth of the tissue extends, according to the depth of the crack and the nature 

 of the contact-surface, over a sometimes larger, sometimes smaller portion of the 

 embedded part of the tendril, and sometimes a callus-thickening is seen to arise 

 even behind the apex, at places where the tendril has adhered closely to a small 

 projection of stone. The thickened end of the tendril clings so firmly to the depres- 

 sion into which it has wedged itself, that it is very difficult to remove it; and here 

 also the attachment seems to be completed by means of a secreted cement. It is 

 seen on examining the parts of the adhesive disc or of the wedged callus-thickening 

 which adhere firmly to the substratum, that the epidermis in particular has under- 

 gone a remarkable change. The epidermal cells are enlarged, drawn out as wart- 

 like protuberances or conical projections, and adapt themselves to all the elevations 

 and depressions of the substratum, grasping even microscopic projections, so that the 

 contact-surface, after being detached by chemical agents, resembles sealing-wax 

 against which a seal has been pressed while it was in a plastic condition. 



It is remarkable that these adhesive discs and growths of callus are only 

 developed after contact with a solid body. If from any cause the tendril is pre- 

 vented from coming in contact with a solid substratum, the growth of tissue, the 

 development of papillae on the epidermis and the secretion of a cement-substance 

 do not occur, and the end of the tendril dries up and dies. This process reminds us 

 strongly of the formation of weals on human skin, and, like this, is dependent upon 

 stimulus, friction, and pressure. 



A spiral torsion occurs in the light-shunning tendril as soon as it has become 

 attached in one way or the other to the substratum. The attached tendrils now 

 become much stronger, and always much more vigorous than those whose apices 

 have not found a resting-place. The stem is now fastened by the elastic tendril to the 

 steep rock face or fissured back of an old tree-trunk. Strong winds may drag the 

 stem somewhat away from the wall, but when they subside it again resumes its 

 normal position, as in the cases previously described, by means of the elastic tendrils. 

 If the stem subsequently grows in thickness the spiral springs holding it are drawn 

 out just as far as is required. Very old stems no longer need their clinging organs; 

 they stand, as strong erect stems, in front of the wall up which they had years ago 

 clambered as young shoots, although their tendrils have now been long dried up; the 

 young shoots alone, always striving higher and higher, still continue to climb up the 

 substratum in the manner described. 



The climbing stem in the restricted sense {stirjjs radicans) holds itself in the 

 normal position attained by growth by means of climbing roots, and uses as supports 



