22 DROSERA ROTUNDIFOLIA. (Guar. II. 
The Inflection of the Exterior Tentacles as directly caused by 
Objects left in Contact with their Glands.* 
I made a vast number of trials by placing, by means of a 
fine needle moistened with distilled water, and with the aid 
of a lens, particles of various substances on the viscid secretion 
surrounding the glands of the outer tentacles. I experi- 
mented on both the oval and long-headed glands. When a 
particle is thus placed on a single gland, the movement of 
the tentacle is particularly well seen in contrast with the 
stationary condition of the surrounding tentacles. (See pre- 
vious fig. 6.) In four cases small particles of raw meat caused 
the tentacles to be greatly inflected in between 5 and 6 m. 
Another tentacle similarly treated, and observed with special 
care, distinctly, though slightly, changed its position in 10 s. 
(seconds); and this is the quickest movement seen by me. 
In 2 m. 30s. it had moved through an angle of about 45°. 
* [The researches of Pfeffer 
(Unters. aus d. Bot. Institut zu 
Tubingen,’ vol. i, 1885, p. 483) on 
the sensitiveness of various organs to 
contact show that the conclusions as 
to the sensitiveness of Drosera cannot 
be maintained in their present form 
(see p. 24). 
Pfeffer shows, both in the case of 
the tendrils of climbing plants, and 
also in that of the tentacles of 
Drosera, that uniform pressure has 
no stimulating action: the effect 
which is ascribed simply to contact 
is in reality due to unequal compres- 
sion of closely neighbouring points. 
Tendrils which move after having 
been rubbed with a light stick fail 
to be stimulated when they are 
rubbed with a glass rod coated with 
gelatine. The gelatine has the same 
uniformity of action as drops of 
water falling on the tendril, which 
are known to produce no effect. If 
the gelatine is sprinkled with fine 
particles of sand, or if the water 
holds particles of clay in suspension, 
stimulation results. Analogous ex- 
periments were made on Drosera 
(p.511). It was found impossible to 
produce movement of the tentacles 
by rubbing the glands with a surface 
of mercury, whereas by rubbing or 
repeated touches with solid bodies 
movement is called forth. Other 
experiments of Pfeffer’s show con- 
clusively that continuous uniform 
pressure has no stimulating effect. 
He placed small globules of glass om 
the glands, and convinced himself 
that, by examination with a lens, 
that contact was affected. Some of 
the tentacles moved, but the majority 
showed no movement, as long as the 
plants were so placed that no vibration 
from the table or floor could reach. 
them. When they were exposed to 
vibration, and when, therefore, the 
glass globules must have rubbed 
against or jarred the gland, the 
tentacles moved. The results de- 
tailed above in the text must pre- 
sumably be set down to the same 
cause, namely, the vibration of the 
table and floor. The sensitiveness of 
Drosera, therefore, by no means ceases 
to be astonishing. Instead of believ- 
ing in movements caused by the 
steady pressure of very small weights, 
we set down the results as being due 
to the jarring of the gland by these 
same minute bodies.—F, D.] 
