E. NESS VARIATION IN INDIAN CORN. 
77 
the ground before the planting of my corn was cow-peas, which were 
/turned under after the vines were dead. 
There is, then, only one difference in the conditions under which the 
two lots of corn were grown that I consider sufficient to produce the 
variation. This difference is the light, which is so much more intense in 
Texas than in New York that no one going from the one State to the 
other can fail to notice it. During the midsummer noonday the glare of 
the light is so intense here that every object seems to assume a glaring 
bright color, and can only be looked at by carefully shading the eyes. 
The black dust of the roads and the ploughed ground look white, and 
the green fields and forests assume something of a silvery, or steel-gray, 
tinge. It must also be borne in mind that since College Station is about 
10° farther south, not only the quantity, but also the quality, of the 
light is different from what it is at Ithaca, N. Y. The light, passing 
almost perpendicularly through the atmosphere here in summer, retains 
nearly all its rays, while in New York, where it passes much more 
obliquely, some of the highly refrangible rays must be obstructed by the 
atmosphere. The difference in season of planting and harvesting between 
the two places would cause that the plants in New York received the most 
perpendicular rays during the very early part of their growth, while in 
Texas this occurred in the latter period of the growth of the plants. 
Whether this would make a difference I am not at present able to say. 
We learn from plant physiology that light, and especially the highly 
refrangable rays of it, have a retarding or stunting effect upon a grow- 
ing plant; that this effect increases with its intensity, and that growth 
will be entirely suspended, if this intensity passes beyond a certain maxi- 
mum. (Vines, Lectures on Plant Physiology, p. 380 and p. 396.) 
A plant grown under light of high intensity is therefore lower, more 
short -jointed, more branched, and has smaller leaves than a plant grown 
under less intense light. (Vines, p. 441.) 
This being the true diagnostics of my corn grown in Texas, I can 
conclude that the main cause of the decrease in the size of stalks and 
leaves, and increase in the number of ears in Indian com when brought 
from a Northern to a Southern latitude, is the increased intensity of the 
light; and perhaps also to the relative greater increase of the more highly 
refrangible rays of that light. 
I regret that this experiment had to be carried on in so crude a way. 
Experiments of this kind carried on here with self -registering apparatus 
for measuring the growth by day and by night, as well as for measuring 
the transpiration for the same periods, would be of the highest value 
to plant physiology, since all such measurements have been made only 
