1904] NEWCOMBE & RHODES: CHEMOTRO?ISM OF ROOTS 27 
IV... THE APPLICATION: OF : CHEMICALS IN ~ BLOCKS: OF “GELATIN, 
The preceding methods all proved themselves unsatisfactory. 
Yet they are worth incorporating in this record, for they are 
methods which would probably suggest themselves to any one 
pursuing this subject, and it is worth while to show the unsatis- 
factory results they bring. 
Another method was conceived which seemed to promise 
better control of the application of a chemical to only one side 
of aroot. This was the employment of gelatin as a vehicle for 
the various chemicals. It was thought that gelatin blocks might 
be made with solutions of salts, and these blocks might be 
brought against the roots, a block on each side. There was, 
however, the question as to the behavior of roots growing in 
gelatin, and their ability to respond to stimuli. Wacker’ 
determined the retardation in the growth of some roots in water, 
while Sachs* and Némec? mention the fact that roots inverted 
in air and water do not return completely to their usual geotropic 
position. Experiments in this laboratory have shown that there 
is a greater retardation of growth of roots in water than in air 
or earth, and a greater retardation in gelatin than in water. At 
the same time, it was found that geotropic response is not so 
great in gelatin as in water, and not so great in water as in earth 
or air. Still growth proceeds apparently normally in gelatin, 
except for retardation; and geotropic responses follow stimula- 
tion, though somewhat slowly. It was decided, therefore, to try 
the use of gelatin. 
Large, rectangular, oblong glass jars were selected to serve 
as damp chambers. They were lined with filter paper, dipping 
into water in the bottom. Paper boxes of suitable size were 
then made, and these laid on glass plates, while their sides were 
held rigid with wooden frames. Into these boxes, as molds, the 
warm. gelatin mass was then poured, and allowed to solidify. 
The gelatin mass had been made by dissolving the dry gelatin in 
a watery solution of the salt to be used on the roots. The 
7 WACKER: Jahrb. Wiss. Bot. 32:71. 1898. 
®Sacus: Arbeiten Bot. Inst. Wiirzburg 1: 409. 1873. 
9NEMEC: Jahrb. Wiss. Bot. 36:89. I901. 
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