^58 SUMMARY OF CURRENT RESEARCHES RELATING TO 
upper side is better protected than the under side against the deposition 
of dew ( Colutea arborescens , Trifolium repens , Impatiens glanduligera, &c.). 
This difference is usually correlated with a difference in the disposition 
of the stomates, as is well seen in the different species of Impatiens ; but 
there are exceptions to this rule. Geotropism no doubt plays some part 
in promoting the vertical nocturnal position. 
Hydathodes are very abundant in the Oxalideee and other nyctitropic 
families. It is probable that the spontaneous movements in the leaflets 
of Desmodium gyrans, Trifolium pratense , and other plants, which have 
no relation to nyctitropism, and the easily provoked trembling of the 
leaves of the aspen, have also an advantage to the plant in promoting 
transpiration. 
Sensitive Cushions of Mimosa.* — In the primary cushions of the 
leaves of Mimosa pudica , Prof. S. Schwendener finds that the stereome- 
sheath which surrounds the central vascular bundle is composed of true 
collenchyme. The “ swelling parenchyme ” has on its inner side a zone, 
consisting of only a few layers of cells, with large intercellular spaces 
which are always filled with air. The larger peripheral portion has 
only very small intercellular spaces. The sensitive (lower) half of the 
cushion has always much thinner cell-walls than the other portion. 
The secondary cushions of the pinnee have essentially the same ana- 
tomical structure as the primary cushions, but the central bundle has 
always a ribbon-like form, and is composed of a collenchyme plate with 
about five vascular bundles lying side by side. On the sensitive side 
of the tertiary cushions are a number of stomates, which are, however, 
not in any way connected with their irritability. The difference between 
the cylindrical central bundle of the primary cushion and the ribbon- 
shaped bundle of the secondary cushions is connected with a difference 
in the mode of curvature. 
The upper and lower halves of the cushiony react in opposite direc- 
tions towards changes in the light. The upper half loses, while the 
lower half gains, in expansive power with loss of light, and vice versa. 
The mathematical conditions of the changes in position are discussed 
in detail. 
(4) Chemical Changes (including Respiration and Fermentation). 
Mucilage Excreted by Seeds.j — According to M. H. Coupin nearly 
all seeds excrete mucilage by a process of osmose when placed in water 
for the purpose of swelling. In the case of peas and haricots, the loss 
of weight by this process may be as much as from two to three per cent. 
The mucilage is derived both from the nucellus and from the integument, 
and the excretion is promoted by a high temperature. 
Secretion by the Scutellum.J — From a series of experiments made 
on the scutellum of grasses (chiefly Zea Mays), Herr J. Griiss has come 
to the conclusion that when the endosperm has been removed during 
germination, the seeds have the power of converting starch into sugar, 
even without the agency of bacteria. 
* SB. K. Preuss. Akad. Wiss. Beilin, xiv. (1897) pp. 228-57 (1 pi.). 
t Rev. Gen. de Bot. (Bonnier), ix. (1897) pp. 241-4. 
j Jahrb. f. wiss. Bot. (Pfeffer u. Strasburger^ xxx. (1897) pp. 645-64 (1 fig.). 
Cf. this Journal, 1895, p. 200. 
