314 BOTANICAL GAZETTE [OCTOBER 
conclusions bear, an attempt i le here to state clearly and tersely LEPESCHKIN’S 
conception of the various processes concerned in the movements by motor organs. 
A change in illumination induces a change in the permeability of the plasma 
membranes for solutes; this results in an alteration of the turgor pressure, which 
of course alters the volume of the opposed halves of the motor organ, and alters it 
in the same fashion, though not at the same rate or to the same extent. Darkening 
reduces permeability, and consequently increases the turgor; lighting has the 
opposite effect. The result of the inequalities of these changes in turgor is a 
curvature of the pulvinus. After this has appeared, diffusion of the solutes begins 
toward the convex side, where the concentration is now lowest in consequence of 
the absorption of water in this half and its expulsion on the concave side; this 
leads to the restoration of the normal concentration of sap and a resultant heighten- 
ing of turgor on the convex side, with a corresponding lowering of it on the other, 
thus intensifying the curvature. Alteration of permeability by changes of illumina- 
tion is not peculiar to motor organs, but occurs also in epidermal cells of Trades- 
cantia and in Spirogyra, where it is proportionally as great, but cannot have the 
Same consequences.t® Of the two movements ordinarily induced by change in 
illumination, the rise or fall of the leaf and the reverse, only the primary movement 
is produced as described; the reverse movement is rather of the nature of an after- 
effect of the primary curvature. Geotropic curvatures of the motor organs are 
explicable on the same principles. The’ physiological dorsiventrality of the 
motor organs is due to the normal direction of gravity. Plants which raise their 
leaves on darkening, have their photeolic movements intensified by being inverted, 
while those that drop their leaves have them reversed by inversion.—C. R. B 
Seedling structure of gymnosperms.—The third paper under this title, by 
Hive and Frarne,'7 treats of the Ginkgoales and Cycadales, and contains the 
usual valuable coordination of scattered results. Under the three heads of 
cotyledons, transition region, and root, the following conclusions are reached: 
otyledons.—The cotyledons, generally two in number, are hypogeal and 
are persistently imbedded in the gametophyte; they are frequently unequal and 
there is a marked tendency to form lobes, and in some cases there is a short basal 
tube; among Cycadales they are more or less closely fused by their ventral sur- 
faces; stomata are generally present, secretory cells and canals are common, and 
the vascular bundles are mesarch or exarch in varying degrees; the number of 
undles in each cotyledon varies from one to eight, in all cases being greater in the 
central region than near the base or tip. 
Transition region —The transition phenomena occur rapidly, so that most of 
the hypocotyl shows root structure; Ginkgo differs from the observed cycads = 
that it has a rotation of the protoxylem of the cotyledonary traces; in Ginkgo 
each cotyledonary bundle gives rise to two poles of the root (except in the case of 
+6 See also TRONDLE, p. 318. 
'7 Hitt, T. G., anp Frame, E. ve, On the seedling structure of gymnosperms. 
II. Annals of Botany 23:433-458. pl. 30. 1909. 
