Hooker.—Hydrotropism in Roots of Lupinus albas. 267 
influence. Vida Faba seedlings were suspended near the surface of a wet 
sponge. The air was saturated and the roots did not bend, so Dutrochet 
decided that hydrotropism did not exist. 
Five years later Johnson ( 17 ) was aroused likewise by E. Darwin’s 
brief statement to test the influence of moisture on roots. An iron wire 
ring, on which was stretched some netting, was fixed in the mouth of an ale 
glass, filled with garden mould, and sown with mustard seeds. As the air 
at the bottom of the glass became moist from contact with the damp 
earth, the radicles grew straight down into it. A hoop was furnished with 
a thread-net bottom, filled with moist soil, and sown with mustard seed. 
As soon as the radicles penetrated the earth and the net, they turned to one 
side and crept along the under surface, perforating the net several times. 
He observed the same result when the seeds were placed in the pores of 
a sponge, fixed in the mouth of an inverted ale glass and cut off flush with 
the brim. Johnson concluded that roots were endowed with some force, 
different from and more powerful than that of gravitation, which compelled 
them to seek moisture. 
Duchatre (8, p. 384) in 1856 gave a detailed criticism of the work of 
his predecessors, He experimented with Chrysanthemum , Hydrangea , and 
Veronica , and found that by keeping the air saturated and the soil dry, 
adventitious roots developed around the base of the stem and showed no 
tendency to descend to earth. Several roots came out of the earth and lay 
on the surface or even ascended into the moist air. 
Van Tieghem ( 32 , p. 325) in 1869 explained the direction taken by 
germinating pollen tubes as due to their sensitiveness to moisture. ‘ The 
pollen tubes finding moisture on only one side, bend in that direction and 
penetrate the stigma.’ The statement was copied by Capus ( 2 , p. 282) 
nine years later. 
Ciesielski ( 3 , p. 25, fig. 5) in 1871 observed that a Zea Mays root laid 
horizontally on a water surface, which wets the under side only, bends 
upward in the usual bending zone. The same thing resulted over a wet 
solid surface, and could be obtained with oat and wheat seedlings as well. 
Ciesielski considered this upward bending to be a phenomenon of growth 
which illustrated a peculiar theory that he was advancing. 
Sachs ( 27 ) reinvestigated the entire field of hydrotropism and placed 
it on a firm and substantial basis. He experimented with roots of Pisum , 
Phaseolus , Vicia, Zea, Helianthus , Tropaeolum , and Ipomaea , and always 
took the precaution of working in a dark room. He found a hanging sieve 
with zinc sides and a cloth bottom the most satisfactory means of obtaining 
hydrotropic bending. It was filled with moist sawdust, sown with seed, and 
hung at an angle of 45 0 . The results agreed with those of Knight and 
Johnson. By hanging the sieve at an angle the projecting root was sub¬ 
jected to a difference of moisture on the two sides, and so bent to that part 
