44 Snow .— The Conduction of Geotropic Excitation in Roots. 
Methods. 
( 
The experiments were made on roots of Vicia Faba^ the Broad Bean. 
The beans were germinated in moist sawdust. The tips were cut off at 
2 mm. from the vegetative point. While being cut, they were held 
horizontal for a few seconds, but in a plane at right angles to that in which 
they were aftewards pinned. For success in the experiment, certain small 
details must next be attended to. A io to 15 per cent, solution of 
gelatine was found the best strength. This was sterilized by boiling and 
a very small drop of it applied warm to the end of the stump with a 
sterilized brush : excess of gelatine spoils the result. The tip can then 
be picked up with another slightly moistened brush and replaced. The 
surface tension of the gelatine pulls it back into position and ensures a good 
fit. The parts next to the cut must not be covered with excess moisture, 
or the gelatine will diffuse away : nor must they be quite dry, or the joint 
may crack open at the edges. The gelatine should not flow over on to the 
sides of the stump. Roots 20 or 25 mm. long were found to serve the best. 
They were placed horizontal after operation, in moist boxes in such a way 
that their geotropic curvatures should be at right angles to the plane of the 
cotyledons, for, as shown by Sachs ( 1871 ), in this plane the root is steady, 
but in the plane of the cotyledons it nutates strongly. The gelatine 
solidifies after a varying time: in several roots that had responded well, it 
was examined in section under the microscope after twenty-four or forty- 
eight hours and found to form a uniform layer about 50 ji thick. There 
had been no growth of the cells to form contact through the layer. 
Most of the experiments were made with beans harvested nearly a year 
previously. Beans harvested in August and used in August and September 
were found less suitable, as they excrete so much water from the end of the 
stump that the gelatine is apt to be washed away. The various operations 
were made with the help of a watchmaker’s lens. 
The results of all experiments were recorded by drawing. 
Section 1. Conduction of Geo-excitation through a Gelatine Layer. 
In the following experiments, only curvatures in the elongating region 
are considered. The various displacements that often take place at the base 
of the root are here omitted as due to other causes. 
(a) Controls. 
3. Thirty-two roots were decapitated and the ends of the stumps 
painted with gelatine, but the tips not replaced. Roots laid horizontal. 
After fifteen to twenty-four hours, 27 had not curved at all, 4 had curved 
down very slightly, 1 had curved down strongly. Even after decapitation, 
therefore, a few roots curve down. 
