ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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being of a less specific gravity than water, owing to the abundance and 
size of its intercellular spaces, this traction ceasing when the leaf has 
reached the surface. A similar explanation, with some modifications, 
can be offered in those cases where the direction of the leaf-stalk is 
oblique rather than vertical to that of the lamina. In no case, he 
believes, is this arrest of growth due to chemical causes, i. e. to the 
difference in proportion of the oxygen in the air contained in solution 
in the water and in the atmosphere. 
Theory of Growth in Height.* * * § — Prof. Weber proposes a mechanical 
theory for the energy of a plant in relation to its growth in height. 
Representing this energy as K, the weight of the plant as P, and the 
height as H ; then K = PH in meterkilograms ; and when K remains 
uniform, P and H are always reciprocals of one another. The author 
believes that the force which determines the mechanical equivalence of 
the annual sum of the work in the movements of the sap must be 
sought for not in “ root-pressure,” but in the merismatic tissue or its 
protoplasm. 
Apparatus for illustrating the Growth of Plants.f — Dr. J. Kiindig 
describes and figures an apparatus which he has constructed for the 
purpose of demonstrating the phenomena of growth in length of plants. 
It consists of a number of metal tubes, arranged one within another in 
telescope-fashion, the uppermost of which represents a growing point 
and the rest internodes of different lengths. The whole is inclosed 
within a box with an opening at the top, through which the system of 
metal tubes emerges by the turning of a key, their successive appearance 
and separation representing the development of the internodes. 
Transpiration and Assimilation.^ — M. Gr. Curtel describes a very 
simple apparatus by means of which the variations in transpiration can 
be studied. A U-shaped tube is taken, and two corks of caoutchouc; 
into one of the corks a capillary tube is inserted, and through the other 
a plant (of rye) is let into one of the arms of the tube. The apparatus 
is filled with water, the corks fixed and waxed, and the variations of 
the column of liquid in the capillary tube indicate the progress of the 
transpiration. 
Assimilation of Carbon by Green Plants.§ — Mr. E. H. Acton has 
conducted a series of experiments in entirely removing the starch from 
the leaves and tissues of growing plants, by placing them either in the 
dark or under a bell-jar with substances which entirely remove all 
carbon dioxide from the air, and then supplying them with various 
organic compounds as food-materials. The general results arrived at 
are that green plants cannot normally obtain carbon for assimilation 
from any substances except carbohydrates or bodies closely related to 
them, not from aldehydes or their derivates, and not even from all carbo- 
hydrates. A compound may be a source of carbon^vhen supplied to the 
leaves, but not when supplied to the roots, and vice versa. Ordinary 
* SB. Bot. Yerein Miinchen, Dec. 9, 1889. See Bot. Centralbl., xli. (1890) 
pp. 10 and 42. f Bot. Centralbl , xli. (1890) pp. 203-5 (1 fig.). 
X Rev. Gen. de Bot. (Bonnier), ii. (1890) pp. 7-16 (1 fig.). 
§ Proc. Roy. Soc., xlvii. (1890) pp. 150-75 (3 figs ). 
2 y 2 
