Gates: THE VALIDITY OF HELIANTHUS ILLINOENSIS 83 
than the normal type. It seems quite likely that this is due to the 
inhibiting action of excessive light upon plant growth. Typical 
plants of this species when growing on sandy soils normally occur 
in the shade. When growing in the sun on the black soil prairies 
of Illinois no deviation from the specific type was observed. In 
the case of the sand prairies of the Beach region the few cases that 
were found showed otherwise. Ina few places where patches of 
this sunflower extended from the sandy soil into the edge of the 
prairie, whose soil, though essentially sandy, was gray on account 
of admixture with humus, the plants growing in the latter situation 
had the appearance of the subspecies while those that were in the 
purer sand remained characteristic of the species. It was very 
evident that both extremes had arisen from the same parent stock. 
This shows the tendency of an increased food supply to produce 
larger plants of the long internode type. The increased pubes- 
cence seems always to accompany the long internodes, while the 
latter may be virtually absent in cases where the former is present. 
Plants growing in sand mixed with humus under the shade of the 
oaks (Quercus velutina) generally responded with longer inter- 
nodes. This was, of course, accentuated in the diminished light. 
The presence of the villous pubescence, which usually is regarded 
as a protection against excessive transpiration, is not so easy to 
understand, for the transpiration under the shade of the oaks is 
obviously not so great as in the open sunlight. As the soil is 
richer and there is no appreciable difference in the water supply, 
it may be that the hairs are produced from an excess of materials 
taken up into the plants, as is suggested by Strasburger for other 
more or less similar cases and for the grit cells of the pear. 
The remaining factor that has the power to influence in the 
production of the subspecific type is the available water-content of 
the soil. A physiological water supply which is too low decreases 
the amount of water available for transpiration, consequently in- 
duces pubescence. Obvious excess of water supply was not 
observed and very likely seldom occurs, as water in the form of 
rain sinks rapidly through the sandy soil of the Quercus velutina 
ridges upon which this Helianthus grows. Normally a sufficient 
supply of the water is left in the sand as films around the sand 
grains. As is very well known, rainfall varies widely both from 
