CLIMBERS, PARASITES, SAPROPHYTES. 197 



have shown that though an extremely slight blow made with a solid 

 body causes coiling (e.g. the shock inflicted by a particle of cotton 

 thread weighing only '00025 of a milligramme and placed on the 

 tendril simply by a draught of air), but that liquids have no effect on 

 tendrils. If water, watery solutions of salts, oil, or even mercury be 

 allowed to fall on a tendril, no coiling occurs, but a response is made 

 if there be any small solid particles in the liquid, e.g. chalk or mud in 

 the water used. Moreover, a tendril is not stimulated by a glass rod 

 coated with gelatine solution, which may be used to strike or stroke 

 the tendril without result. This fact has led to some astonishing 

 results in experiments, glass rods coated with gelatine being used to 

 hold the tendril and to study the effects of different stimuli. 



Blows inflicted by solid bodies cause coiling, but no effect is pro- 

 duced by mere continuous pressure ; thus, if smooth glass threads, 

 or a needle, be pressed carefully against the tendril, without friction 

 and without any sudden increase in the pressure, no coiling occurs, 

 though coiling at once results if these bodies are gently rubbed against 

 the tendril. These facts are of biological interest, for they show that 

 tendrils cannot be stimulated by rain or by general shaking of the 

 plant by wind. 



The general growth and behaviour of tendrils can be studied in the 

 Sweet Pea, but those of Passion-flower or White Bryony are more 

 suitable for experiments. 



Why does a Sweet Pea seedling fall over and sprawl about if no 

 support, e.g. a stick, is placed near it ? Place sticks in a pot of seed- 

 lings, also strings stretched between sticks and running horizontally 

 and at different angles. Are the tendrils able to coil around horizontal 

 supports as well as inclined or vertical supports ? Sketch a young leaf 

 with tendrils which have not yet come into contact with a support : 

 are the young tendrils straight or curved ? Is it possible to make a 

 young tendril coil without providing it with a support ? Try the effect 

 of stroking a young tendril with a stick, a string, a glass rod ; stroke 

 it at different points. Which part of the tendril is sensitive to contact 

 and responds by coiling ? 



Choose a tendril of Passion-flower or White Bryony which has its tip 

 slightly hooked, and with a pencil rub the inner side of the hook 

 (lower surface of tendril) for about a minute. The tip should at once 

 begin to coil, and in about two minutes the terminal 15 ram. will 

 probably form a ring. 



Many of the facts stated above can only be demonstrated by skilful 

 manipulation, but it is easy to prove that a smooth body has no effect 

 on a tendril. Dissolve two sheets of Marshall's sheet gelatine in a 

 quarter pint of hot water, and dip into it a smooth rod of glass or 

 wood about 3 mm. in diameter. Rub the cooled rod against a tendril. 

 No effect is produced when the gelatine- cove red part is used, but 

 coiling occurs when the tendril is stroked with the uncoated part. It 

 is an advantage to use two rods, touching the convex side of the 

 tendril, which is not sensitive, with one rod and thus holding it owing 

 to the stickiness of the gelatine, while the other rod is used for 

 stroking the tendril. 



