April 20, 1882] 
NATURE 
379 
gined it to be strictly accurate ; but Wiesner shows that it is 
possible, by taking some pains, to make it very inaccurate.! 
But the arrangement given in Wiesner’s diagram is one 
which no one would think of employing, if he wished to 
make the best of the method; in all our experiments we 
tried, as far as possible, to avoid the extremely oblique 
arrangement chosen by Wiesner. This may toa large 
extent be ensured by placing the fixed mark as near 
the base of the plant as possible, z.e. when tracing on a 
horizontal plane the movements of a vertical organ ; if 
when the stem of the plant is vertical, the index attached 
to the plant is vertically above the fixed mark, then 
growth vertically upward will be represented by a single 
dot. By taking reasonable pains in making some such 
arrangement, I still believe that no very serious error will 
be introduced. 
In the second method of observing ’ circumnutation, 
a glass filament bearing two small sights was fixed 
to the plant, and its position was recorded by making 
a dot on a glass plate in line with the two sights. 
Against this method no such serious charges can be 
brought, and it was largely used, and was, as matter of 
fact, preferred by us. The methods given by Wiesner 
are in many ways, no doubt, preferable to those employed 
for “‘ The Power of Movement,” and are in principle the 
same as that described by mein the Bor. Zeztzng, 1881, p. 
473, which consisted in estimating the actual position of the 
moving point by means of a vertical microscope; Wiesner 
has also employed a vertical tube without lenses. In the 
latter case, the position of the tube is varied until the 
cross wires are vertically over the observed point, and the 
various positions of the cross wires at successive intervals 
of time can be recorded in a way we need not stop to de- 
scribe. In the case of the microscope the movements are 
recorded by means of the eye-piece micrometer. This 
a tt 
yl 
a 
FIGI. 
Fic. 1.—Diagram representing a plant which is supposed to increase in 
length by the portions a4, 4c. Mand N represent microscopes for ob- 
serving the direction of growth. 
method requires to be treated fairly and not to be bur- 
lesqued ; it presupposes a knowledge of the general direc- 
tion in which the growth of the organ under observation 
is proceeding, and the microscope should be parallel to 
this direction. If as in Fig. 1 a plant grows straight from 
a@ to 3, it will be seen by the microscope M, moving in the 
direction of the arrow ;* growth from 4 to ¢ will not be 
* Tt may, however, be observed that if the plant in Wiesner’s diagram had 
grown straight on in the original direction, the tracing given would have 
been a straight line, and we should have drawn the correct conclusion that 
the plant was not circumnutating. 
2 Or rather in the reverse direction, owing to the reversal of the image by 
he microscope. 
perceived as lateral movement, but as growth towards the 
observer, and the same is true ziztatis mutandis for the 
microscope N. Thus if we estimate the whole lateral 
movement which has taken place during the growth from 
a toc by the two microscopes M and N, we shall see that 
they give reverse results. It will therefore be seen that 
the same general knowledge of the direction of growth is 
required for Wiesner’s and for our method, and that unless 
this knowledge is properly utilised, either method can be 
made to give wrong results. 
In a notice like the present, it is impossible either to 
give or to attempt to answer all Wiesner’s criticisms, 
and in what follows I cannot do more than notice what 
seems to me the more important points. Wiesner states 
that circumnutation is not nearly so generala phenomenon 
as we believe it to be. That growth in a perfectly straight 
line (with a qualification to be mentioned hereafter) is 
found to occur, and therefore that circumnutation is not 
an essential quality of growth, is not, in fact, an “ Urbe- 
wegung ” (Primordial-movement). 
Let us first consider the circumnutation of roots. The 
observations given in “ The Power of Movements’’ on 
this head were made by two methods. In some ca:es 
a glass fibre (P. of M., p. 10) was fastened by shellac- 
varnish to the tip of the root, and the movements of the 
end of the glass fibre were then recorded by making dots 
on a glass plate. In other cases the tip of the root was 
made to inscribe its course on the smoky surface of an 
inclined glass plane. By this means curious wavy and 
broken lines were drawn on the glass plates, which we 
believe to afford evidence of circumnutation. Wiesner 
confirms the results, but differs entirely in the conclusions 
which he draws. He believes that the coating of soot is 
the cause of the apparent circumnutation. He believes 
that the soot acts injuriously on the root, and causes it to 
curve away from the injured side, by means of the spe- 
cialised sensitiveness which, as we have shown, enables a 
root to curve away when the tip is injured by caustic, &c. 
He supports this view by an experiment in which (Wiesner, 
p. 166) the inclined glass plate was coated with semen lyco- 
podit instead of soot, and he always found that the course 
described was a straight unbroken line. This experiment 
is strongly in favour of Wiesner’s view; but, on the 
other hand, I fail to see how Wiesner’s explanation ap- 
plies to the lateral movements of the root’ which gives the 
waviness to the course traced, although it may legiti- 
mately be used to explain the movements away from the 
smoky surface which cause the line to be often a broken 
one. 
The other observations on the circumnutation of roots 
recorded in “ The Power of Movement” are set aside by 
Wiesner among other reasons, because they were made by 
fastening a glass filament to the tip of the root, a method 
which, as he states, disturbs the growth of the root and 
causes an apparent circumnutation. Moreover, Wiesner’s 
own observations, made with a microscope, lead him to” 
disbelieve in the existence of circumnutation in roots. 
Wiesner says (p. 174) that the circumnutation of roots is 
due to the antagonism between geotropism and the natural 
tendency to curvature existing in the root (Sachs’ curva- 
© The lateral movements are probably explained by Wiesner as the result 
of the antagonism of geotropism and that tendency to nutation which we call 
Sachs’s curvature. 
