a enon 
114 The Botanical Gazette. [March, 
The distance between the point of contact with the plant 
and the pivot is one-fortieth of the distance from the black- 
ened glass rod to the pivot, so that any growth of the plant 
is magnified forty times on the blackened rod. Thus a growth 
of one-thousandth of an inch will be represented by one- 
twenty-fifth of an inch on the blackened rod. 
From the blackened glass rod a permanent record can be 
obtained by making a print of it on sensitized paper, from 
which direct measurements can be made. 
The instrument was devised and made by my brother, M. 
J. Golden, professor of practical mechanics in Purdue Univer- 
sity. 
The following observations are given to show the work 
done by the apparatus. 
Record of experiments. 
The study of growth in length has received a great deal of 
attention from many physiologists, notably Sachs. He has 
found that there is a maximum and a minimum point of 
growth, and also that there are forms of growth for which no 
reason, as yet, has been assigned, these latter being termed 
‘‘spontaneous variations.” Growth in length has been studied 
for small as well as large plants, but in no recorded case has 
growth in thickness been studied upon any but large plants, 
and in these the measurements were made by the observer at 
intervals of time with some calipering instrument, thus intro- 
ducing a possible error due to the personal equation. The 
periodicity of growth has been determined for growth if 
length, but has been assumed for growth in thickness, largely 
as a result of measurements of growth in length and as am 
accompaniment to it. / : 
The amount of tension is one of the principal factors in 
growth, as there is little growth when the tension is low, 4? 
greatest growth when the tension is high. Kraus' has found 
in his measurements on stems of trees that there is a re 
growth have been found to occur by other investigators. But 
he states that he has found that temperature has very little 
effect on tension for the ordinary variations occur betweel 
10-30°C. In his experiments on the tension of stems 
*Kraus, G., Die tagliche Schwellungsperiode der Pflanzen 28. 
