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 grooving Internales. 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: — 
1. Cimicifuga 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 
Original length 
of internode. 
296 mm. 
26 
65 
102'5 
242 
33'5 
252-5 
71-5 
226 
Amount of temporary 
elongation. 
6-8 p.c. 
i8-o 
3-1 
•8 
4'4 
2'2 
10-4 
1- 8 
6-3 
2- 6 
Amount of perma- 
nent elongation. 
3'5 p.c. 
5 '4 
1*1 
•o 
I'O 
•4 
i'5 
•4 
3'5 
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. 
(Z>) 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 curvature. 
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. 
Length of the 
internode. 
Valeriana officinalis ; stalk of 
young inflorescence. 
Before bending . 
1. Bent . 
2. Bent in opposite direct 
3. Bent as in (i) 
4. Bent as in (2) 
Straightened 
Cimicifuga racemosa. Before 
bending 
1. Bent . 
2. Bent in opposite direct 
Straightened 
Heracleum sibiricum ; stalk o 
umbel. Before bending 
1. Bent . 
2. Bent in opposite direct 
curvature 
when bent. 
cm. 
4 
4 
4 
4 
Radius of cur- 
vature when 
left to itself. 
cm. 
13 
21 
23 
24 
201'5 
165 
165*5 
165-5 
19 
22 
18 
23 
Thickness of 
the middle part 
of the internode. 
6 mm. 
* 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. 
