180 SUMMARY OF CURRENT RESEARCHES RELATING TO 
determined their elective power of absorption of the salts of certain 
mineral elements over those of others. Thus the presence of potassium 
will greatly lower, or even reduce to zero, the absorption of sodium. 
(3) Irritability. 
Geotropic Irritation-Movements.* — Prof. F. Czapek compares the 
movements of irritation in plants with the reflex movements in the 
animal kingdom, even in respect to the different periods into which they 
may be divided. The period of impact he terms the “presentation 
period,” that between the commencement of the irritation and the com- 
mencement of the reaction is the “ reaction period ” ; the “ impression 
period ” is that during which an organ retains the capacity to react to 
an irritation, when prevented from executing its movement at the moment 
of irritation. The geotropic presentation period extends, as a rule, to 
about 15 minutes at 25° C. ; the heliotropic presentation period is shorter, 
i.e. plants are more quickly sensitive to light than to gravity. The 
sensitiveness increases with a rise of temperature. Chemical reagents 
act in a similar way. 
Microscopic investigation has failed to detect any difference between 
an irritated organ and one not irritated. Microchemical examination, 
on the other hand, indicates an increase, under the influence of geotropic 
stimulus, of aromatic oxidisable, and a decrease of oxygen-carrying sub- 
stances (in root-tips and the apex of the cotyledons of grasses), but this 
is not the case with heliotropic stimulus. 
By the term JEsthesia the author expresses the capacity of an organ 
to respond to definite physical stimuli ; it may take the form of “ photo-,” 
“ geo-,” or “ chemo-sesthesia.” The phenomena of this reaction may be 
classed under the following heads : — (1) Taxis or movement (“geo-” or 
“ photo-taxis ”) ; (2) Tropism or curvature ; (3) Strophism or twisting ; 
(4) Trophy or increase in thickness ; (5) Auxesis or new formation of 
organs ; (6) Stasis and Dolichosis, the acceleration or retardation of 
growth in length. The author further adopts Sachs’s term Anisotropy 
for the inequality in the external response to reaction. 
Irritable Movements in Marantaceae.j-— Mr. C. H. Thompson de- 
scribes some movements in the flower of Marantaceas ( Maranta , Calathea, 
Thaliai), which are evidently adaptations for promoting cross-pollination. 
In all the species one of the staminodes is developed into a keel-like 
structure, which at maturity enfolds the stylo. On the margin of the 
keel, about midway between the apex and the base of the staminode, is 
a tentacle-like body, which is extremely irritable. In the open flower 
this tentacle guards the way to the flower. When the tentacle is 
irritated, the impulse is conveyed to the sheathing base of the keel, 
opening it, and allowing the style to escape. The style forms a semi- 
circle, and the stigma violently strikes the visiting insect which has 
irritated the tentacle, or that part of its body which has already become 
dusted with pollen. 
* Janrb. f. wiss. Bot., xxxii. (1898) pp. 175-308 (7 figs.). 
t Acad. Sci. St. Louis, Oct. 17, 1897. See Bot. Gazette, xxvi. (1898) p. 371. 
