HOAV PLANTS CLIMH. 



809 



exist in all stages of passage, from a full-sized and non-sensitive blade to 

 nothing but a highly sensitive midrib. 



The course of development, then, seems to be as follows : — First, by 

 circumnutation contact is maintained, then supersensitiveness is excited ; 

 adaptive growth and development, with alteration of structure, follow, 

 and the climbing organ is finally produced in the course of generations. 

 When once formed, the organ, with its properties, becomes an hereditary 

 feature. 



Good illustrations of this last result are the two commonly grown 

 species of Ampelopsis. A. hecleracea, the Virginia Creeper, has a tendril 

 constructed out of a flowering branch. It makes the feeblest attempts: 

 to climb round any foreign support; but as soon as the little hook-like 

 extremities of the branchlets of the tendril can catch any roughnesses in 

 a wall, the effect of contact is soon seen. Not only do they swell inta 

 little pads, but secrete an adhesive substance ; while the branchlets curl 

 up like irregularly formed corkscrews, and thicken greatly. That all this 

 is the actual result of contact is seen by the fact that if any tendrils fail 

 to secure a hold they soon fall off. 



In A. Veitchii, the Japanese species, the tendrils have their pads 

 already partially developed in an immature condition, before any contact 

 is made at all ; so that the one species throws light upon the other, ia 

 that not only is the power to produce the pads hereditary (as in A. 

 Jicderacea), but the actual result has become anticipatory in the latter 

 species, just as an eye is formed before it can feel the effect of light. 



The climbing property, having become inherent in the constitution 

 and hereditary, may be held in abeyance, but be still potentially there. 

 Thus, dwarf French Beans make strong stems and have no need to climb ; 

 nevertheless, they occasionally throw out a long shoot which twines round 

 any support. Certain species of Ipomcea, allied to Convolvulus, of South 

 Africa, never climb in the wild state, but when transferred to Dublin took 

 to climbing at once. Perhaps the most remarkable is a tree called 

 Riptagc. This is grown in gardens in Cairo. It has a fair-sized trunk,, 

 with thick branches. Suddenly a long whip-like shoot appears and twines 

 up anything it can come across. As it belongs to the o^d^ev Malpighiacecey 

 which has several climbing Lianes, it is a tree whose ancestors evidently 

 were accustomed to climb, and has retained the power though it is quite 

 useless, for the tree is perfectly well able to support itself. 



