1907] DOUGLAS—INTUMESCENCES ON POTATO 249 
the under side in these patches was killed. No intumescences were 
formed on the old plants. On the new plants. in two days a few 
intumescences formed as follows. On the first shoot sprayed with 
copper nitrate a few intumescences were produced over the veins. 
On the second shoot a few were formed on the surface. On one 
shoot sprayed with copper ammonium carbonate a few intumescences 
appeared at the tip of a leaf. The potato plants which were used, 
however, were not very healthy ones and developed from poor, 
shriveled, small tubers. These shoots would not form intumes- 
cences under bell jars when supplied with water, which fact was 
probably due to the leaves being poorly supplied with glucose. Had 
healthy young plants been used, it is very possible that intumescences 
would have been readily produced. 
SUMMARY 
Intumescences are produced on young potato plants from good 
tubers, when transpiration is checked and the roots are absorbing 
water. Their formation is increased by conditions which favor an 
increased absorption of water, as a warm soil, and is prevented by 
the opposite condition of a cold soil. 
Intumescences are formed abundantly both in bright light and in 
weak light, which shows that light acts as a stimulus to their produc- 
tion only so far as it provides for the normal metabolism of the shoots 
and leaves. 
Intumescences are not produced in total darkness, as this condition 
favors the rapid elongation of cells in the stem, which can thus make 
use of an increased supply of water. At the same time there is less 
of the osmotically active substance present in the leaves in darkness 
as photosynthesis is not taking place. 
The abnormal state of turgescence of the hypertrophied cells is 
probably due to the osmotic action of glucose, assimilated in part 
by the leaf, but principally supplied to it from the underground tuber, 
so richly provided with starch. 
In conclusion, I wish to acknowledge the many helpful sugges- 
tions of Professor ATKINSON, under whose direction this work was 
undertaken. 
CoRNELL UNIVERSITY 
