652 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
manifested itself, and are tlien put in an erect position and illuminated 
on the previously lower side, they will be affected by the light as 
rapidly as jdants which have stood erect. On the other hand, plants 
which were first stimulated by light were much more slowly affected by 
geotropism acting in an opposite direction. This law applies, however, 
only to plants or organs that are strongly heliotropic. The “heliotropic 
angle,” i.e. the angle of incidence at which light has the most stimulating 
effect, varies with the species. When an orthotropic organ is acted on 
by both stimuli — light and gravitation — the resultant curvature will 
depend not only on the relative force of the two stimuli, but also on the 
position of the organ. 
Sensitiveness of Plants.'* * * § — Dr. F. Noll gives a resume of the present 
state of our knowledge with regard to the sensitiveness of plants to stimu- 
lation from external forces, — light, heat, gravitation, contact, chemical 
forces, &c. 
(4) Chemical Changes (including Respiration and Fermentation). 
Physiology of Germination.! — Dr. J. Griiss adduces further evidence 
in favour of the view that, in germination, a diastase passes from cell 
to cell, a new reagent having been employed for the detection of this 
diastase, viz. : — guiacum-hydrogen-peroxide. By its use three different 
kinds of diastase can be discriminated, viz. : — translocation-diastases,, 
secretion-diastases, and glucase ; cytase forming a doubtful fourth class* 
A peculiar change in the cell-wall by the action of diastase is de- 
scribed under the name alloolysis, which was followed out in the date- 
seed. The first stage in this process consists in the ferment penetrating 
the cell-wall, this being usually followed by a transformation of the 
cellulose. The hydrolytic change in the hemi-celluloses which compose 
the cell-wall may be recognised by the following characters : — the 
refringency decreases, the cellulose becoming hyaline ; the double re- 
fraction in polarised light is reduced ; the behaviour towards staining 
reagents undergoes a change ; the solubility on addition of acids is 
decidedly increased. 
Vegetable Digestion.! — As the result of experiments made on the 
residue left after extracting the root-hairs of plants with water, M. V* 
Poulet states that they invariably contain iron, and he believes this to 
be the essential element in the process of digestion, thus establishing a 
close analogy with the same process in animals. But, while the iron 
in the gastric fluid of animals is in the form of peptonate, that present 
in the roots of plants occurs as tartrate. The aqueous extract has 
sometimes a neutral, sometimes a feebly acid reaction. 
Disappearance of the Contents from Reserve - Receptacles. § — 
According to Herr K. Puriewitsch, the disappearance of starch and 
other carbohydrates from reserve-receptacles is not necessarily due to a 
* Ber. Senckenberg. Naturf. Gesell., 1896, pp. 169-257. 
f Landwirthsch. Jakrb., xxv. (1896) pp. 385-452 (2 pis. and 1 fig.). See Bot. 
Central bl., lxvii. (1896) p. 364. Cf. this Journal, ante, p. 544. 
X Comptes Rendus, cxxiii. (1896) pp. 356-8. 
§ Ber. Deutsch. Bot. Gesell., xiv. (1896) pp. 207-12. 
