ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
515 
nutation of a young stem resemble those of all non-climbiug stems. 
They consist of a succession of more or less irregular circular or 
elliptical curves, varying every moment even in their direction, caused 
by the unequal lengthening of the zone of growth of the stem. In 
the case of Ipomaea , the authors were able to determine a distinct 
heliotropism. The violet and ultra-violet rays exercise a distinctly 
prejudicial influence on the unrolling of the stem. White light retards 
the growth both of climbing and of non-climbing stems. 
A movement of circumnutation was distinctly determined in roots, 
and one more regular even than that of the stem This is the case 
also with a number of aerial roots, such as those of Orchidese, Aroideaa, 
and Bignoniaceee. 
The sleep-movements of a number of leaves were observed, both 
those in which the movement of the leaflets is an upward, and those 
in which it is a downward one. In both cases the movement is by no 
means an uninterrupted one, but consists of a number of alternate move- 
ments upwards and downwards, at first considerable, then much less 
pronounced ; the former of these are termed by the authors movements 
of oscillation, the latter movements of trembling. 
(4) Chemical Changes (including Respiration and Fermentation). 
Urease.* — M. P. Miquel describes a new diastase which according to 
the nomenclature of Duclaux is called urease. This ferment is secreted 
by those bacteria capable of converting urea into carbonate of ammonia. 
Urease is obtained from peptonized bouillon cultivations to which 
2-3 grm. per litre of carbonate of ammonia have been added. The 
ferment, isolated by filtration, is capable of converting 60 to 80 grm. 
of urea into carbonate of ammonia per hour. It is much more delicate 
than other known diastases, its efficiency being much impaired even at 
50° in a few hours, and destroyed in a few minutes at 75°, though it 
will keep for weeks at a temperature of about 0°. 
The author has cultivated about forty species capable of trans- 
forming urea into carbonate of ammonia. All of these cultivated in 
bouillon devoid of urea secrete this diastase, and he infers that the 
alkaline fermentation of urea is always due to its action. 
On the action of this ferment is founded a method for the quantita- 
tive estimation of urea. If a vessel containing equal volumes of a urea 
solution and of bouillon impregnated with urease be kept at 50°, all the 
urea will be converted in two hours. If the alkalinity before and after 
this procedure be determined, this will give the amount of ammonia 
produced, and hence the quantity of urea present. 
Cellulose-dissolving Enzyme.f — Mr. H. T. Brown has found, from 
experiments on various animals, pigs and horses, that the destruction of 
the vegetable cell-membrane during digestion is owing to its being 
dissolved in the stomach by a cytohydrolyst pre-existent in the grain 
before ingestion. 
The author started from the fact that the cell-walls were observed 
to be breaking down before the gastric contents had passed through the 
* Comptes Rendus, cxi. (1890) pp. 397-9, 501-2. 
f Journ. Chem. Soc., cccliii. (1892) pp. 352-64. 
2 n 2 
