ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
497 
another instance of a similar phenomenon in Larrea cuneifolia, a shrub 
from the Argentine Republic. He distinguishes two different varieties of 
the phenomenon, politropism, in which the position assumed is always 
a meridional one, the two surfaces facing east and west, and parortlio- 
tropism, in which the lamina assumes a vertical, but not necessarily a 
meridional position. The latter condition may be a stage of transition 
to the former, and either may be brought about by different causes, such 
as heliotropism or geotropism. 
(4) Chemical Changes (including Respiration and Fermentation). 
Respiration of Plants.* — In a long series of experiments Dr. C. 
Stich has carefully investigated the effects on respiration of a diminished 
pressure of oxygen, and of injuries to the tissue. As a general result it 
was found that the activity of the intramolecular was in inverse propor- 
tion to that of the normal respiration ; so that, even with a very great 
reduction of the proportion of oxygen in the surrounding atmosphere, 
no very great reduction ensued in the amount of carbon dioxide produced. 
In a general way also the effect of different kinds of injury on various 
parts of plauts was to increase the activity of the respiring process. 
This is partly dependent on the increase of surface exposed to the air 
resulting from the injury. 
Respiration in the interior of massive tissues.f — According to 
M. H. Devaux, such tissues as those of the beet and the potato are not 
so dense as to prevent the access of the atmospheric air to every cell in 
the interior of the organ. The gases imprisoned in such organs always 
contain a large proportion of oxygen, and respiration takes place in the 
normal way. The air gains access through a system of branching canals 
which permeate the tissue in every direction, and which allow of the 
rapid passage of gases, even when there is but a slight difference of 
pressure. 
Composition of the internal Atmosphere of Plants.^ — According to 
a series of observations made by M. J. Peyron, the proportion of oxygen 
in the air contained in the tissues of plants is subject to great variations ; 
the amount is always less than that in the surrounding atmosphere, 
while that of carbon dioxide is considerably greater. The proportion of 
oxygen shows two minima, between 7 and 9 a.m., and between 4 and 5 
p.m., and two maxima, about noon and between midnight and 1 a.m. The 
night maximum is usually greater than that in the day ; and these varia- 
tions are independent of the time of year, of the temperature, and of 
chlorophyllous assimilation. Young leaves usually contain less oxygen 
than mature leaves, and those fully exposed to light less than shaded 
leaves ; evergreen generally contain more than deciduous leaves. Move- 
ments in the air increase the amount of oxygen in leaves. 
Influence of the Carbohydrates on the Formation of Asparagin.§ — 
Herr N. Monteverde has attempted a solution of this question by 
* Flora, lxxiv. (1891) pp. 1-57 (2 figs.). 
f Comptes Rendus, cxii. (1891) pp. 311-3. 
X ‘Rech. sur 1’atmosphere interne d. plantes,’ Corbeil, 1888, 89 pp. See Bot. 
Centralbl., xlv. (1891) p. 217. 
§ Arb. St. Petcrsb. Naturf.-Vcr. (Bot.), xx. pp. 28-30, 43-5 (Russian). See Bot. 
Centralbl., xlv. (1891) p. 379. 
