22 HooKER: PHYSIOLOGICAL OBSERVATIONS 
since it is a reaction in response to differences existing on the ; 
opposite sides of the tentacle. The inflexion and expansion of a | 
Drosera tentacle present a remarkable instance of a practically — 
continuous reaction, produced by a single mechanism, but caused — | 
by two stimuli of different nature, so that it is partly nastic and — 
partly tropic. 
iii. Growth and Turgidity 7 
Since the movement of a Drosera tentacle is the result of 
growth, it is always longer at the end of a reaction than at the ~ 
beginning. The amount of elongation varies from 0.1 mm. to _ 
0.5 mm. This suggests a simple demonstration to show that the 
reaction is accompanied by growth. If a single tentacle on a 
leaf is stimulated, it will project a noticeable distance beyond its — 
fellows after regaining its original position. In the field, a Drosera 
leaf frequently has some tentacles longer than other ones in the ; 
same row. These inequalities are the result of growth attendant — 
upon reaction, for all the tentacles in one row remain of equal : 
length if not stimulated. Sometimes a small insect is caught by — 
a single exterior tentacle, which carries it to the center of the leaf. 4 
The insect is, however, too minute to cause a sufficient impulse to” | 
be conducted from the discal to the other marginal tentacles. — 
They do not bend, so that after the reaction is completed they are — 
not as long as the tentacle which was inflected. : 
Turgidity does not play a part in the movement of the ten- | 
tacles. This was proved by plasmolyzing bent tentacles in 20 — 
per cent salt solution. The plasmolyzed tentacles remained bent. — 
A comparison of Fics. 4, 5 and 8 with graphs of Fitting, which 
show the haptotropic reactions of tendrils of Sicyos angulatus | 
(Fitting, ‘02, p. 378), of Passiflora gracilis (Fitting, '03, p. 577, 
fig. 6) and of Pilogyne suavis (ibid., p. 578, fig. 7), shows that the © 
mechanics of movement in tendrils and tentacles are the same. 
Similar figures are shown by Wiedersheim for photonastic reactions | 
of leaves of Impatiens parviflora (Wiedersheim, ’04, p. 241, fig. I; 
Pp. 242, fig. 2; p. 244, fig. 5), and for thermonastic reactions of the 
perianth leaves of the tulip (ibid., p. 250, fig. 8) and the crocus 
(tbid., p. 254, fig. 10; p. 255, fig. 12). It is clear that all these - 
reactions are produced by the same mechanism; rapid growth on | 
the convex side and in the median section with attendant contrac- | 
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