24 HooKER: PHYSIOLOGICAL OBSERVATIONS 
of all the tentacles. Those which remain inactive at one time, 
might bend on a subsequent occasion. However this may be, no i 
tentacle has been observed to react the fourth time. 
The second and third reactions of a tentacle are essentially — 
similar to the first. After two reactions a tentacle is much less — 
sensitive than before, as is shown by the increased reaction time. 
Each subsequent bending takes longer (cf. C. Darwin, ’08, p. 19), 
but the original position is regained in approximately the same — 
time. The amount of growth does not vary according to any 
definite rule. It depends rather on external conditions and is 
apparently uninfluenced by the age of the tentacle. If the 
external conditions are constant, the amount of growth remains 
the same. In one example (TABLE VIII) this was approximately 
the case, the increase in length for the first, second and third 
‘ reactions being 0.16 mm., 0.18 mm. and 0.14 mm. respectively. 
The region of growth is however more restricted in each 
subsequent reaction, and is confined to more basal portions of the 
tentacle. TasBLe VII shows that 57 per cent of the tentacle grew 
in length during the first inflexion, 50 per cent during the second, 
and 32 per cent during the third. In another instance (TABLE 
VIII) the regions of growth were successively 70, 53, and 27 
per cent of the length of the tentacle. In each reaction a certain 
portion of the tentacle becomes fully grown. A Drosera tentacle 
is therefore characterized by intercalary, basipetal growth. Be- 
cause of this, the number of inflexions which a tentacle can make 
must necessarily be limited. It is therefore highly probable that 
a tentacle would bend a fourth time only under very exceptional 
circumstances. 
Since growth is limited to more basal regions, the thickness of 
the reacting portion is greater at each successive inflexion. More- 
over the greatest difference between the lengths of the opposite 
sides tends to decrease. Both of these factors cooperate in reduc- 
ing the amount of bending, so that the gland is moved through 
successively smaller angles, as shown in Fig. 11. 
vi. Nastic reactions 
In all the experiments described, the glands of the marginal 
tentacles were stimulated directly, but reactions follow likewise 
ES 
a ere cee ine ae oes 
