SEPTEMBER 27, 1918] 
The conductivity of phosphorescent cal- 
cium sulphide was later separately investigated 
at the University of Heidelberg, and it was 
shown that certain wave-lengths not in the 
infra-red gave a maximum effect, which was 
contrary to what one might have expected 
from Lenard’s theory. Rather the effect was 
a maximum near the point where the photo- 
electric effect stopped, suggesting some relation 
between the photoelectric and actinodielectric 
effect. An investigation of the relation be- 
tween these two effects (which amounts to 
finding out the relation between the ease with 
which the electrons are ejected and the in- 
erease in conductivity for different wave- 
lengths of light) was started for sulphur, dur- 
ing the summer of 1913, by the writer at the 
Davy-Faraday Research Laboratory of the 
Royal Institution, London, England, but was 
not finished. 
The relation between the photoelectric effect, 
actinodielectrie effect and phosphorescence has 
been discussed by the writer and a general 
theory of phosphorescence has been developed 
which includes fluorescence, fluorescent X- 
rays, organic phosphorescence and self-lumi- 
nous radioactive substances.2 In the review 
of this theory in the “ Beiblatter zu den An- 
nalen der Physik” the difference between 
Lenard’s theory of phosphorescence and the 
author’s is not clearly pointed out. The au- 
thor’s theory takes into account resonance, 
Stokes’s law and a critical energy content, 
which is not done by Lenard. 
In conclusion, in respect to phosphorescent 
ealeium sulphide, it should be said that red 
light does increase its conductivity, but does 
not give a photoelectric effect. 
Cuester ArTHUR BuTMAN 
SPECIAL GROWTH-PROMOTING SUBSTANCES 
AND CORRELATION 
THE vigor of potato sprouts bears a direct re- 
lation to the size of the seed piece, or in other 
words to the amount of tissue surrounding the 
eye. When a certain minimum is reached, the 
vigor of the sprouts decreases as the size of 
2See ‘‘The Electron Theory of Phosphores- 
cence,’’ Physical Review, 1912. 
SCIENCE 
319 
the seed piece is reduced. The weak, slender 
sprouts produce correspondingly weak plants 
which remain weak during their entire period 
of growth and yield a small crop of tubers. 
The weak sprouts are not due to lack of 
usual food materials, as sprouts on pieces still 
large enough to contain an abundance of these 
substances, show considerable decrease in vigor. 
Tf a lack of sufficient ash constituents is re- 
sponsible for the weak sprouts, they might be 
expected to approach their usual vigor if the 
small pieces be allowed to sprout in rich soil, 
as the sprouts form roots very quickly in moist 
soil. The sprouts from such pieces, however, 
do not gain any vigor under these conditions. 
It seems logical to conclude that the potato 
tuber contains a limited amount of a special 
growth-promoting substance and if the amount 
of tissue surrounding the growing bud is too 
small, there is not enough of this substance 
available for normal growth. 
Some of the experimental data is included 
in Bulletin No. 212 of the Maryland Agricul- 
tural Experiment Station under the following 
title: “ Physiological Basis for the Prepara- 
tion of Potatoes for Seed.” While this bulletin 
was in press an article appeared by Loeb, in 
which he states that equal masses of sister 
leaves of Bryophyllum calycium produce ap- 
proximately equal masses of shoots in equal 
time and under equal conditions, even if the 
number of the shoots varies considerably. He 
concludes that the limited amount of material 
available for growth and the automatic attrac- 
tion of the material by the buds which grow 
out first, explain the inhibiting effect of these 
buds on the growth of the other buds. 
If the correlative inhibition of bud growth 
on the potato tuber has a chemical basis it does 
not appear to be identical with the growth- 
promoting substance which the writer has pos- 
tulated and which seem to effect the growth of 
sprouts only after they have started. Several 
facts in connection with the growth of sprouts 
on potato tubers could be mentioned to sub- 
stantiate this conclusion but the two following 
experiments seem sufficient. 
If a potato tuber bearing vigorous sprouts 
on the terminal end is cut transversely into 
