GENERAL PROPERTIES OF GROWING PARTS OF PLANTS. 703 



dit!on of growth imjjarts greater elasticity and firmness to the tissues. Under the 

 influence of gravitation they then grow more rapidly on the lower side, become 

 upriglit, and raise up the still greater weight of the fruit ; as is strikingly seen 

 in Friiillaria imperial is, Anemone pra/ensis, and many other plants with pendent 

 flowers and erect fruits. In other cases again the curvature, which was at first 

 due merely to external causes, becomes permanent and fixed in the tissue itself 

 b\' the processes of growth, as in the fruit-stalks of Solanum Dulcamara. 



One of the most striking phenomena of this class is that a blow on the side 

 of a rapidly growing internode causes it to assume a curvature which lasts for a 

 considerable time. The same thing occurs when the upper part of a shoot is 

 taken in the hand and a curvature imparted to it similar to that caused by the 

 blow. The upper part acquires in consequence a pendent position which may 

 however be again neutralised by subsequent growth. 



There has been as yet no exact or detailed investigation of the elasticity of 

 growing shoots, roots, and leaves ; and the enquiry is, as I have convinced myself, 

 attended with considerable difficulty. Observations sufficient to enable us to study 

 some of the phenomena of vegetation to be described in this chapter can however 

 be made with the simplest methods and apparatus. 



ici) Exknsibilily of groiving Inlernodes. The upper and lower end of an 

 internode of a freshly cut fragment of a stem were marked with Indian ink. The 

 shoot was held above and below the marks, laid on a micrometer graduated to 

 millimetres, and stretched as strongly as possible without breaking'. The result 

 is shown in the annexed table : — 



Name. 



1. Cimiei/'uga raeemosa 



2. Sambucus nigra 



The next older internode 

 A still older internode 



3. Aristolochia Sipho 



The next older internode 



4. Aristolochia Siplio 



The next older internode 252 



5. Aristolochia Sipho 



The next older internode 226 



Imperfect as was the method of observation, these figures nevertheless show 

 (i) that growing internodes are highly extensible, (2) that extensibility decreases 

 with age, (3) that elasticity increases with age. 



{b) Elasticity to flexion of groiving Internodes. Internodes of fresh turgescent 

 shoots were cut off, and bent on a card on which concentric circles were drawn; 

 the axis of the internode was made to coincide as nearly as posssible with one of 



^ This somewhat primitive method of stretching, which of course does not furnish an exact 

 measure of the extensibility of different internodes, was employed because stretching by means of 

 weights necessitates fastening the shoot, which is attended with great inconveniences. 



