282 Hooker. — Hydrotropism in Roots of Lupinus albus. 
per cent, agar were prepared, and to one of them NaCl was added in 
the proportion of 1-015 gr. per 100 c.c. The two solutions were poured 
into tumblers and allowed to solidify. The agar blocks were then removed, 
cut smoothly down the middle, and the half blocks paired, so that each 
tumbler held one half with and one without salt. Of 20 roots placed 
between these half blocks, 1 6 were bent into the salt-free block after seven 
hours. This reaction would naturally be considered chemotropic, but 
its analogy to hydrotropism and osmotropism is striking, and raises the 
question whether many of the results obtained and classed as chemotropic 
are not in reality of an osmotropic nature. 1 
Summary. 
1. Roots of Lupinus albus are always positively hydrotropic. 
2. Hydrotropic reactions occur in roots only between 80 and 100 
per cent, relative moisture. 
3. The minimum moisture difference to which roots react at 20° C is 
a fall of o-2 per cent, per cm.; the optimum is 0-4 per cent, per cm. ; the 
maximum is 0-5 per cent, per cm. 
4. Under optimum conditions six hours elapse before hydrotropic 
reaction is visible in roots. A presentation period could not be determined. 
5. The hydrotropic sensitivity of roots resides chiefly in the tip, 
but also to a lesser degree above the root-tip. 
6. Two factors determine the reaction of the root to a hydrotropic 
stimulus ; one mechanical and the other vital. The intensity of the reaction 
varies inversely as the former and directly as the latter. When the stimulus 
is weak, the vital factor predominates; when too intense (above the 
maximum) the mechanical factor determines the reaction. 
7. Hydrotropism is not a special case of traumatropism, but is probably 
equivalent to osmotropism. 
Sheffield Scientific School. 
Bibliography. 
Those works marked with an asterisk (*) were not obtainable in the original. 
1 . Bonnet, Ch. ( 1754 ): CEuvres d’histoire naturelle. Vol. ii. Recherches sur l’usage des feuilles. 
Paris. 
2 . Capus, G. ( 1878 ) : Anatomie du tissu conducteur. Ann. d. sci. nat., Bot., 6 e ser., t. vii, 
pp. 209-91. 
3 . Ciesielski, Th. ( 1871 ): Untersuchungen fiber die Abwartskriimmung der Wurzel. Cohn’s 
Beitr. z. Biol. d. Pfl., Bd. i 2 , pp. 1-3, PI. 1, Figs. 1-5. 
4 . Darwin, Ch. ( 1880 ^ : Power of Movement in Plants. London. 
5 . Darwin, E. ( 1800 ) : Phytologia ; or the Philosophy of Agriculture and Gardening. London. 
6. DETLEFSEN, E. M. ( 1881 ) : Uber die von Ch. Darwin behauptete Gehirnfunklion der Wurzel- 
spitzen. Arb. d. bot. Inst, in Wurzburg, Bd. ii, pp. 627-47. 
1 Cf. Porodko, Uber den Chemotropismus der Pdanzenwurzeln, Jahrb. f. vviss. Bot., Bd. xlix, 
1911, p. 347, Tabelle 17. 
