ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
199 
Elseagnus, Alnus , and Podocarpus resemble Leguminosse in their power of 
assimilating the free nitrogen of the air by means of root-nodules. 
Negative results were obtained from a series of experiments on mustard, 
buckwheat, and oat. 
(3) Irritability. 
Photeolic Movements and Structure of Pulvini.* — Mr. F. De F. 
Heald proposes the term photeolic for the movements in vegetable organs 
due to the varying intensity of the light. The organ (pulvinus) the 
curvatures of which set in motion other passive organs, is called the motor 
(in contrast to the motile) organ. This organ is termed the primary, 
secondary, or tertiary, according as it is at the base of the primary 
jjetiole, or of the petioles of the primary or secondary pinnae. A de- 
pression which often occurs in the centre of the stele of the motor organ 
is termed the hilum of the stele. 
With one exception among the plants observed ( Abutilon Avicennsef 
simple leaves never have pulvini. In the case of compound leaves, if 
a primary pulvinus is present, there are always also secondary pulvini, 
The pulvinus is never provided with stomates, and has but very few 
intercellular spaces ; these, when present, are very small. This gives 
the pulvinus a darker colour than the ordinary tissue. The cells contain 
either chlorophyll or xanthophyll. The epiderm is well developed, and 
is usually covered with trichomes. Tho completely developed organ is 
always traversed by a stele which is entire, and completely surrounded 
by a layer of non-lignified bast-fibres. It always shows, even in the 
diurnal position, well-marked transverse folds, which become changed 
when the curvature of the organ increases or diminishes. 
Traumatropic Curvature of Roots.f — Prof. Y. M. Spalding has 
investigated, in the case of the root of seedlings, secondary roots, and 
aerial roots ( Anthurium ), the phenomena termed by Pfeffer traumatropism , 
i. e results which follow the infliction of wounds on the tip of growing 
roots. If a radicle is branded just below the apex, the tip begins, in 
the course of an hour or more, to bend away, so that in a few hours 
the lower part of the radicle is strongly convex on the injured side. In 
the course of a day or two the tip may have described an entire circle. 
This traumatropic curvature is independent of a quite distinct mecha- 
nical curvature which takes place at the spot where the injury is inflicted, 
and which is concave on the injured side ; it follows only when the 
injury is close to the apex. The experiments made show that the tissue 
lying just beneath the root-cap is sensitive, and that the wound gives it 
a stimulus to which, after induction, the root responds by bending. No 
traumatropic curvature takes place even when extensive injury is inflicted 
which does not involve the growing point. The biological significance 
of the phenomenon appears to be that it removes the wounded portion 
of the root from the source of injury while repair is going on. 
Fall of the Corolla of Verbascum.f — Sig. U. Martelli explains as 
a phenomenon of irritability the fact that in all species of Verhascum 
examined, the corolla of mature flowers becomes detached and falls 
* Bot. Gazette, xix. (1894) pp. 477-91 (1 pi.). 
t Aim. Bot., viii. (1894) pp. 423-51. 
; Journ. Linn. Soc. (Bot.), xxx. (1894) pp. 316-22 (3 figs.). 
