1910] CURRENT LITERATURE 71 
Chemotropism of roots.—In a preliminary paper, PoropKko® reports upon 
the chemotropism of the roots of Lupinus albus and Helianthus annuus. Roots 20- 
35 mm. long were placed in a lamella of agar varying in thickness from 6 to 60 mm., 
which separated the solution used from water. In all, 50 chemical substances 
were used, the concentration of which varied from 0.1” to o.co1m. As a rule, 
the roots did not remain straight, but bent against or with the diffusion stream. 
The range of concentration between maximum and minimum depended upon the 
substance used and the thickness of the agar lamella. Concentrations close to 
the maximum caused bending against the diffusion stream or positive response, 
which effect was observed with both electrolytes and non-electrolytes. PoropKo 
considers this a traumatropic response, due to the inhibition of growth on the 
up-stream side of the root. With lower concentrations, electrolytes and non- 
electrolytes affect the roots differently. The former cause great regularity as 
regards the direction of bending of the root, while the latter produce positive, 
negative, and intermediate responses. Acids, alkalies, and carbonates cause 
positive, and neutral salts negative bendings. The responses due to H and OH 
ions are considered to be traumatropic. The amount of negative response seems 
to depend upon the cation, being greater in the presence of one with a double 
charge than in the presence of one with a single charge. In many cases the 
responses are not all of one kind, Nevertheless, it is necessary to explain the 
cause of all. From his experiments, Poropxko concludes that positive but not 
negative responses can take place in decapitated roots, and that the latter, but 
not the former, show up as after-effects, although only on the clinostat. The two 
reactions are different in nature, the positive being passive and caused by the 
inhibitory effect of the greater concentration on the growing region on the up-stream 
side of the root, the negative being active and due to the chemotropic effect of the 
diffusion stream, which tends to accelerate the growth on on ae up-stream side. 
Hence, upon the growing region of a root of Lup d to the influence 
of the diffusion stream of a chemical ibetdrine, two aittaponistic tendencies are 
at work, the direction of bending of the root being dependent upon the relative 
strengths of the two tendencies. Roots of Helianthus annuus act differently 
from those of Lupinus albus, in that they show only traumatropic response, but 
why this is true is not known.—R. CaTLIn Rose. 
National Academy of Sciences.—At the annual session of 1910 two botanical 
papers were presented (April 19), which may be outlined as follows: 
“The distribution of Agave in the West Indies,” by WILLIAM TRELEASE.— 
Three main types of Agave are recognized in the West Indies: one confined to the 
southwestern Cuban region, another to the Inaguas, and the third ranging through 
the entire archipelago. Subtypes of the latter are limited respectively to the 
Greater Antilles, the Bahamas, the Caribbees and the Leeward Islands, and the 
§ PoroDKo, THEOopoR, Ueber den Chemotropismus der Wurzel. Ber. Deutsch. 
Bot. Gesell. 28:50-57. IQIO. 
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