16 Lioyp: LEAF WATER IN GOSSYPIUM 
this condition* has been demonstrated quantitatively above, the 
minimum amount being found, in these determinations, at the 
10 hour or somewhat later. It becomes evident that the opening 
of the stomata is accompanied by a net loss of water by the leaf, 
more being given off by transpiration than can be obtained to 
replace it, as I have shown to occur by comparative volumetric 
and gravimetric determinations in Fouquieria splendens.t The 
results of similar experiments with cotton may be said, in an- 
ticipation of their publication, to harmonize fully with those 
on Fouquieria. 
Concerning the relative behavior of young and old leaves 
it may be further pointed out, that so far as the evidence goes in 
the present paper there is little against either of the alternate 
views that this loss of leaf water is better resisted by the young or 
by the old. The numbers of stomata per unit area in the young 
leaves are considerably greater. An important inquiry at this 
point is in regard to the relative extent of the internal evaporating 
surfaces, t but though we do not find the answer, we may be sure 
that it is sufficient in young leaves to lead to wilting, and that the 
stomata do not head eff the net loss during the period of advancing 
temperature, insolation, and evaporating power of the air. 
It is quite possible that determinations of the amount of 
leaf water at smaller intervals of time would lead to the finding that 
the loss is more sudden, after it once begins, in old leaves than 
in young ones, and that this may be connected with the relative 
diffusive capacity of the stomata in consecutive intervals of time. 
I have arrived at this suggestion by a comparison of the dimen- 
sions of the slightly open pores of young and old stomata, and 
by calculating their relative diffusive capacities.§ It develops 
that in old stomata the edges of the pore are more stiffly reinforced, 
and that in opening they separate from each other throughout 
t Bergen, J. Y. Relative transpiration of old and new leaves of the Myrtus 
§ Livingston, B. E., and Estabrook, A. H. Observations on the degree of 
stomatal movement in certain plants. Bull. Torr. Club 39: 15-22. 12 F 1912. 
