484 
SUMMARY OP CURRENT RESEARCHES RELATING TO 
by means of a number of haustorium-tubercles, of which the largest 
attain a diameter of 5 mm. ; it attacks the stem, leaves, and root in the 
underground zone of the host, but not the root-tubercles of Lotus or 
Medicago. 
Transpiration-current in Plants.* — Herr T. Bokorny finds the most 
convenient method of tracing the course of the ascending current in a 
plant to be by causing it to absorb small quantities of iron sulphate (not 
more than 0*1 per cent.), and then precipitating by potassium ferri- 
cyanide. 
By this method he has determined that the elements through which 
the greater part of the conduction of water takes place are the vessels 
(and the tracheids of Conifers), a current being always perceptible in the 
cell-cavity ; whether there is also any considerable conduction through 
the walls, he leaves undetermined. A current through the walls appears 
to take place in some cases, but not in others. The pith often gives 
strong lignin-reactions, and is therefore quite incapable of conducting 
water. The water also appears to rise through the prosenchymatous 
cells of the xylem, through those of the sclerenchyme, through the thin- 
walled bast, and through the collenchyme. The ascent through the 
sclerenchyme and collenchyme appears to tell against Sachs’s imbibition- 
theory. In the upper portions of the stem of Nicotiana and Cucurbita 
the walls of the vessels alone were found to contain iron. In N. rustica 
the water had risen to the extent of 1 metre in three-quarters of an hour. 
Passage of Gases through Plants.f — Prof. J. Wiesner and Dr, H. 
Molisch give the following as the chief results of a series of experiments 
on this subject. 
Gases subject to pressure are unable to penetrate by filtration either 
through the cell-wall, whether living or dead, whether dry or saturated 
with water, or through the protoplasm or watery cell-sap. The move- 
ment of gases from cell to cell can take place only by diffusion when 
the tissue is a close one, or also through the intercellular spaces where 
these occur ; the rapidity of diffusion is in proportion to the quantity of 
water imbibed by the cell-wall. Dialysis of dry air cannot take place 
to any determinable amount through cell-walls when they are neither 
lignified nor suberized ; but it can take place through lignified or 
suberized cell-walls. Carbon dioxide diffuses through cell-walls more 
rapidly than hydrogen, oxygen, or nitrogen, the rapidity of diffusion 
being proportional to the absorption-coefficient and the density of the 
gas. Carbon dioxide passes out of vegetable cells by diffusion more 
rapidly into air than into water. Periderm is more hygroscopic, and 
imbibes water more rapidly, than had previously been supposed. 
(3) Irritability* 
Movements of Nutation. f — Dr. A. Hansgirg distinguishes several 
kinds of nutation, especially in connection with petals and leaves, viz. : — 
The ephemeral and periodical nutation-movements of petals, which 
* Jahrb. f. Wiss. Bot. (Pringsheim), xxi. (1890) pp. 469-503. 
f SB. K. Akad. Wiss. Wien, xcviii. (1889) pp. 670-713. 
x Oesterr. Bot. Zeitschr., xl. (1890) pp. 48-53. 
