78 MR. DARWIN ON CLIMBING PLANTS. 



way from it. Hence the sweep of the lower part of the tendril 

 of the Hanburya is much restricted. Here a nice case of co- 

 adaptation conies into play: in all the other tendrils observed by 

 me the several branches become sensitive at the same period ; had 

 this been the case with the Hanburya, the rectangular spur-like 

 branch being pressed, during the revolving movement, against the 

 projecting end of the shoot, would infallibly have seized it in a 

 highly injurious manner. But tho main tendril, after revolving 

 for a time in a vertical position, spontaneously bends downwards ; 

 and this, of course, raises the rectangular branch, which it sill* 

 also curves upwards ; so that by these combined movements the 

 spur-like branch rises above the projecting end of the shoot, and 

 can now move freely without touching it ; then, and not until then, 

 it first becomes sensitive. 



The tips of both branches, when they come into contact with a 

 stick, grasp it like any ordinary tendril. In a few days after- 

 wards the inferior surface swells and becomes developed into a 

 cellular layer, which adapts itself closely to the wood, and firmly 

 adheres to it. This layer is analogous to the adhesive disks 

 formed by the tips of the tendrils in some species of Bignonia, 

 but in the Hanburya the layer is developed along the terminal 

 portion of the tendril, sometimes for a length of 1£ inch, but not at 

 the extreme tip. The layer is white, whilst the tendril is green, 

 and near the tip it could sometimes be seen to be thicker than the 

 tendril itself; it generally spreads a little beyond the sides of the 

 tendril, and its edge is fringed with free elongated cells, which 

 have enlarged globular or retort-shaped heads. This cellular 

 layer apparently secretes some resinous cement ; for its adhesion 

 to the wood was not lessened by immersion for 21 h. in alcohol or 

 water, but was quite loosened by the action during the same period 

 of ether and turpentine. After the tendril has once firmly coiled 

 itself round a stick, it is difficult to imagine of what use the for- 

 mation of the adhesive cellular layer can be. Owing to the spiral 

 contraction, which ensues after a time, whether or not the tendril 

 has clasped any object, it was never able to remain, excepting in 

 one instance, in contact with a thick post or a nearly flat surface ; 

 if it could have become attached to such objects by means of the 

 adhesive cellular layer, this layer would evidently have been of 

 service to the plant. I hear from Dr. Hooker that several other 

 Cucurbitaceous plants have adherent tendrils. 



Of other Cucurbitacerc, I observed in Bryonia dioica, Cucurbit a 

 ovifera, and Cucumis sativa, that the tendrils were sensitive and 



