Hydrotropism in Roots of Lupinus albus. 
BY 
HENRY D. HOOKER, Jr. 
Osborn Botanical Laboratory , Yale University, New Haven , Connecticut. 
Introduction. 
S INCE it was shown in a previous paper ( 16 ) that the phenomena com¬ 
monly called thermotropic in roots were due largely to hydrotropism, it 
seemed advisable to investigate this tropism more in detail, and to determine 
to some extent the laws which govern it, and the limits within which it acts. 
The subject is of more particular interest because the question of the 
limitation of hydrotropic sensitivity to the root-tip has never been definitely 
settled since Darwin first suggested it. The work was done for the most 
part during the summer semester of 1913 at the University of Strassburg 
under the guidance of Professors Jost and Kniep, whose invaluable assis¬ 
tance I wish to acknowledge here. The work was finished at the Osborn 
Botanical Laboratory of Yale University at New Haven, Connecticut, under 
Professor Evans, to whom I am likewise indebted for much help. 
History. 
The idea that roots enter the earth to seek moisture necessary for 
growth is one of those popular conceptions that are of venerable age because 
they are easily and naturally thought of. It was consequently offered as 
an explanation of those phenomena which we now call geotropic. Later, 
when botanists began to comprehend the nature of this latter reaction, the 
possibility of hydrotropism was questioned and experiments made which 
seemed to disprove its existence, for these two tropisms were then thought 
to be alternative. The study of hydrotropism has therefore experienced 
but slow development amid numerous set-backs, although its history has 
been relatively long. 
As early as 1700 Dodart ( 7 ) tried to explain the directions taken by 
the root and shoot, as determined by the materials they need. He thought 
roots were made of fibres which shortened when acted on by the earth’s 
moisture and lengthened when warmed by the sun’s rays, while the stem 
[Annals of Botany, Vol XXIX. No. CXIV. April, 1915.] 
