784 



MECHANICS OF GROWTH. 



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

 be made with the simplest methods and apparatus. 



(a) Extensibility of gronuing Internodes. 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. Cimici/uga racemosa 



2. Sambucus nigra 



The next older internode 

 A still older internode 



3. Aristolochia Sipho 



The next older internode 



4. Aristolochia Sipho 



The next older internode 



5. Aristolochia Sipho 



The next older internode 



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 gro^'ing 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 possible with one of the circles ; 

 the radius of this circle is recorded in the following table as the radius of cur'vature. 

 The internode was then left to itself, and its permanent curvature determined in the 

 same manner. The branch was then bent on the other side, and so on, as shown 

 by the table. The internode was finally laid with its concave side on the measuring 

 rod and pressed straight on to it. 



* 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. 



