CHEMICAL AND PHYSICAL CHANGES IN GEOTROPIC 
STIMULATION AND RESPONSE 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 179 
Eva O. SCHLEY 
(WITH SIX FIGURES) 
Considerable work has been done on chemical-physical changes 
involved in tropic presentation and reaction. Kraus (1) was 
probably the first worker in this field. His researches include the 
determination of (a) the sugar content of the growing shoot, 
(b) the relation of the sugar maximum to the growth maximum, 
(c) acidity in the growing shoot, and (d) steps in the change of the 
cell-content of the two halves (the shoot was split longitudinally 
into the concave half, the inside of the curved portion, and convex 
half, the outside of the curved portion, of the responded organ) 
of the shoot exposed to geotropic or heliotropic stimuli during per- 
ception and reaction time. He found that (a) the sugar in the grow- 
ing shoot increases for a certain region from above downward 
and then decreases, (6) the sugar maximum lies below the growth 
maximum and consequently is not the limiting factor in growth, 
(c) the acidity is greatest in the tip and decreases downward. In 
geotropically and heliotropically stimulated shoots he found, first, 
decreased acidity and increased sugar on the convex side, later, 
an increase of water and decrease of sugar on the convex side, 
followed by a decrease of acidity on this side. 
CzaPexk (2) working with geotropically stimulated roots found 
an interference with the oxidation of tyrosin and phenylalanine 
which led to the production of homogentisic acid. GROTTIAN (3) 
and GRAFE and LINSBAUER (4) were unable to confirm his results. 
Martin Fiscuer (5) has shown that the water-absorption power 
of colloids is increased by the addition of acids and alkalies up to 4 
certain concentration, and that salts decrease this power. PROMSY 
(6) has found that organic acids increase the growth rate of seed- 
lings. Ravin (7) likewise found that acids increase the rate of 
Botanical Gazette, vol. 56] [480 
