1911] CURRENT LITERATURE 469 
gidium if 2-valved would be a Draba; while the Californian genus Tropido- 
carpon has one species with 2-valves and one (T. capparideum Green) with 4. 
Tetracarpellary cultivated varieties of Brassica and Isatis are also known. 
Such instances as these, of the recurrence of similar characteristics in more 
or less closely related species or genera, support the view that variation is 
definite or “‘orthogenetic” rather than entirely fortuitous. The author 
believes that such facts are directly opposed to the older conception that 
Species, genera, and families have a monophyletic origin. On p. 280 the 
gametic formulae of the reviewer’s forms, Capsella bursa-pastoris tenuis and 
C. bp. rhomboidea, are transposed; and on p. 304 the date of the discovery of 
C. Heegeri is stated erroneously as 1907 and 1908, the correct dates being 1897 
and 1898.—GeEo. H. SHULL. 
Geotropism and epinasty.—KNIeEPS has studied in detail the part played 
by geotropism and epinasty in the orientation of certain foliage leaves. He 
makes much use of modified forms of the oblique and intermittent clinostats 
of Firtinc. With these instruments Firtmnc® answered conclusively many 
questions on the geotropism of orthotropic organs that two or three decades 
of work with other instruments had left unanswered. Now, KNiep proceeds 
to clear up a number of questions in a plagiotropic organ, the leaf. 
In the main Lophospermum scandens was used, for the medium-aged leaves 
of this plant show.no sleep movement and little tendency to dark rigor; there- 
fore, they are well adapted to experimentation in darkness. When leaf 
blades of this plant are placed out of their normal rest position, they recover 
it by growth-bending of the petiole. During the bending the rate of growth 
of the middle line is greatly increased. KNtep designates the usual position 
of the leaf as the normal horizontal position. If the plane of the blade is so 
changed that the petiole end remains in the original plane but the apical end 
falls below it, the angle it forms with the normal horizontal position is said 
to. be negative. If this displacement continues — 180°, the leaf is then in the 
inverse horizontal position. By a reverse movement from the normal horizontal 
rest position a positive displacement is brought about. ‘If this gh aan 
continues +180°, the inverse horizontal position is reached. If in dark- 
ness a plant is so tilted that a leaf blade takes a position of —1°—114°, a rapid 
growth sets up on the morphologically lower side of the petiole (concave bend- 
ing) and the blade finally acquires its normal horizontal position. If the 
plant is so tilted that the blade holds any position from —116° to + 180°, or 
from +1° to +180°, rapid growth begins on the upper side of the petiole 
(convex bending) and the leaf finally acquires its normal horizontal position. 
The labile rest position, then, is at approximately —115°. 
5’ Kntep, Hans, Ueber den Einfluss der Schwerkraft auf die oe der 
Laubblatter ‘wad der Frage der Epinastie. Jahrb. Wiss. Bot. 48:1-72. 1910 
° Jahrb. Wiss. Bot. 45:675-700. 1905. 
