ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
55 
readies it exactly symmetrically in reference to tlie various intensities 
of light. It follows that the part of a plant exposed to diffused day- 
light must receive an infinitely large number of light-impulses ; but 
the action of these impulses is largely negatived in relation to the 
direction of growth of the organ, so that those impulses only are 
effective which are not neutralised by an equivalent impulse in the 
opposite direction. 
Influence of Light on the Form and Structure of Branches.* — 
Observations made by M. Maige on the Virginian creeper and the ground- 
ivy lead to the following general conclusions. Diffused light favours 
the formation of climbing or creeping branches, and may cause the 
transformation of a flowering shoot into a climbing or creeping shoot ; 
while direct light produces the contrary effects. Diffused light, acting 
on climbing or creeping branches, increases in them the morphological 
and anatomical characters which adapt them to climbing or creeping 
habits ; while direct light produces the contrary effect. 
Influence of Gravity and Light on the Dorsiventral Structure of 
Branches.f — From experiments, chiefly on the branches of the umbel 
in the Umbelliferas, M. H. Ricome concludes that solar radiation in- 
tensifies the characters proper to an assimilating tissue on the side 
facing the light. The action of gravity is shown in the unequal size 
of the cells of oblique branches ; they are larger on the side facing the 
light. The combined influence of light and heat determines the form 
of the branch. The illuminated surface is usually the upper surface. 
This is the cause of the frequent folding of the upper surface of many 
pedicels, the object of which is to increase the surface occupied by the 
assimilating tissue in the furrows, and to allow at the same time of the 
development of the supporting tissue at the sides. This combined 
influence greatly modifies the arrangement of the vascular bundles. 
The dorsiventrality of the oblique branches of an inflorescence must 
be regarded as a radiar structure modified by the combined influence 
of solar radiation and gravity. 
Rectipetality.J — An example of this phenomenon — the tendency of 
an organ to straighten itself after having been curved by the action of 
an external irritation — is recorded by Herr F. G. Kohl. Growing stems 
of Allium atropurpureum and Tradescantia virginica — the former con- 
sisting of a single, the latter of many internodes— were laid horizontal, 
and allowed to erect themselves by the agency of geotropism. In the 
former case the erect stems remained curved, while in the latter case 
they became nearly straight. The author lays stress on the fact that it 
is only in the nodes that geotropic, heliotropic, and other kinds of irri- 
tation can arise, though they can be propagated through the internodes. 
(4) Cliemical Changes (including Respiration and Fermentation). 
Changes in Oily Seeds during Germination.§ — From experiments 
made chiefly on Arachis and Ricinus, M. L. Maquenne has come to the 
* Comptes Rendus, cxxvii. (1R93) pp. 420-3. 
f Tom. cit., pp. 436-9 (2 figs.). Cf. this Journal, 1898, p. 209. 
X Ber. Deutsch. Bot. Gesell , xvi. (1898) pp. 169-73 (2 figs.). 
§ Comptes Rendus, cxxvii. (1898) pp. 625-8. 
