822 SUMMARY OF CURRENT RESEARCHES RELATING TO 
of one or more layers lying immediately beneatli tlie epiderm to which 
he gives the name “ root-liypoderm.” The outermost layer of this 
hypoderm, lying immediately beneath the epiderm, frequently consists 
of two different kinds of cell, shorter and longer, and may be compared 
to the “ velamcn ” of the roots of the Orchidese. The longer cells of 
this layer appear to serve the purpose of the absorption of the sap, the 
shorter ones that of the storing up of nutrient materials. 
Apparatus for Determining the Periodicity of Koot-pressure.* — 
Mr. M. B. Thomas has invented an apparatus for this purpose. It 
consists essentially of a tin cylinder with smoked surface, and a U- 
shaped tube containing mercury, on which floats an indicator which 
marks the smoked surface of the cylinder, the cylinder being made to 
revolve by means of clockwork. The apex of the cut stem of the plant 
is inserted into an inverted U-shaped tube, which is connected with the 
larger one; and the supply of water to the plant is maintained by means 
of an inverted flask, the tube of which touches the surface of the water 
in the dish in which the pot is placed. As the root absorbs water the 
pressure upon the column of mercury increases, and lifts up the indi- 
cator, which marks a continuous spiral line on the cylinder. 
Assimilation of Free Nitrogen by Plants.f — Herr B. Frank deals 
in the present paper with the differences in this faculty displayed by 
different species, and with the value of the process in agriculture. 
He points out that a clear distinction must be drawn in the first 
place between the power of a plant to accumulate nitrogen in an agricul- 
tural sense, and its power to assimilate free nitrogen from the air in 
a physiological sense. Those plants which are known as “ nitre-plants” 
possess the former of these properties to a high degree, drawing large 
quantities of nitrogen from the nitrogenous compounds in the soil, but 
the latter property only to a small extent ; while many leguminous 
plants, such as Lupinus luteus, display the latter characteristic very 
strongly, but the former hardly at all. Nitrogen-accumulating plants 
are those only which contain, when mature, more nitrogen than they can 
have obtained from the soil. Between these plants and those which 
consume nitrogen, a hard and fast line cannot, however, be drawn for 
practical purposes. The value of different soils for the accumulation of 
nitrogen by different species of plants is treated in detail. 
The author repeats his assertion, and confirms it by further experi- 
ments, that the assimilation of free nitrogen from the air is a very 
widely distributed phenomenon in the vegetable kingdom, and is by no 
means confined to the Leguminosaa. It does not, however, take place 
until the vegetative organs have attained a considerable vigour. Neither 
leguminous nor non-leguminous plants contain in their seeds a sufficient 
supply of nitrogenous compounds to enable the seedling to reach that 
stage at which this direct assimilation of nitrogen takes place ; and they 
are therefore dependent on the nitrogen compounds in the soil ; or, in 
the case of the Leguminosae, on the faculty which is imparted to them 
by the symbiotic fungus BJiizobium, Leguminosarum. The author does 
* Bot. Gazette, xvii. (1892) pp. 212-4 (1 pi.). 
t Landwirtbsch. Jahrb., xxi. (1892) pp. 1-44. See Bot. Centralbl., 1. (1892) 
p. 269. Cf. this Journal, ante , p. 511. 
