632 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
non-parasitic green plants have, however, to a large extent, lost the 
power of using such substances as a source of carbon. The author 
considers that his experiments do not settle the question whether the 
immediate result of the mutual decomposition of carbon dioxide and 
water by plants is formic aldehyde. 
Cause of the Movement of Water in Transpiring Plants.* — Dr. J. 
Boehm adduces additional arguments in favour of his view that the 
absorption of water in transpiring plants is not due primarily to endos- 
motic action in the root, or to differences in the pressure of the air. 
The absorption of water through the roots, and the ascent of sap are, on 
the other hand, in his view, a capillary function of the vessels, which 
may be regarded as a continuation of the capillary spaces in the soil. 
The ascent of sap takes place only in the outermost alburnum, and is 
exceedingly rapid when transpiration is excessive. The sap-conducting 
vessels of Conifers are the tracheid bundles, the elements of which are 
in open connection with one another. 
Transpiration.']' — Herren E. & J. Verscliaffelt state that, other con- 
ditions of light, temperature, &c., being the same, transpiration is greater 
in an air containing no carbonic acid than it is in the ordinary atmo- 
sphere. 
(3) Irritability. 
Chemotactic Irritability 4 — Herr B. Stange has made a series of 
observations on the sensitiveness to the presence of various chemical 
substances of the zoospores of Saprolegniaceae and the myxamoebae of 
Myxomycetes. The results confirm de Bary’s general statement that 
parasitism and sapropliytism are influenced by the chemical composition 
of the host or medium. 
The experiments on Saprolegniaceae were made on a species belonging 
to the Saprolegnia ferax group, grown, with due precautions, on the dead 
bodies of flies. They determined the fact that, while certain other sub- 
stances exercise a smaller or greater attractive or repulsive influence on the 
zoospores, it is the phosphates in the decaying body of the insect or in 
the nutrient fluid, and not the compounds of nitrogen or carbon, which 
excite most strongly the sensitive movements of the zoospores ; and there 
is, for this purpose, an optimum concentration for phosphoric acid itself 
and for each of its salts. No other free acid produced the same effect. 
Whether the effect is attractive or repulsive depends on the concentration 
of the solution. Neither free oxygen nor variations of temperature had 
any considerable influence on the irritability. 
The Myxomycetes observed were chiefly Chondrioderma difforme and 
JEthalium sejoticum. The results differed materially from those obtained 
with Saprolegnia. Phosphoric acid and its salts, citric acid, tannic acid, 
glycerin, cane-sugar, and other substances exercised no attractive force 
on the myxamoebae of Chondrioderma ; on the other hand, malic and 
* Verhandl. K. K. Zool-Bot. Gesell. Wien, xl. (1890), Abhandl., pp. 149-60 
(3 pis.). Cf. this Journal, 1886, p. 824. 
f Bot. Jaarboek (Gent), ii. (1890) pp. 306-24 (2 pis.). See Bot. Centralbl., xlii. 
(1890) p. 373. 
x Bot. Ztg., xlviii. (1890) pp. 107-11, 124-7, 138- 42, 155-9, 161-6. 
