438 BOTANICAL GAZETTE [DECEMBER 
more than double for Physalis and less than double for the 
onic, = 
12. The Clements instrument, with “‘solio” paper, seems to be 
generally about three times as sensitive as are these plants, some- 
what more than this for Xanthium and Martynia, somewhat less 
for Physalis. From these averages it appears more sensitive than 
by the method of frequencies; see 6 above 
On the whole, we may conclude that the black and brown 
atmometers and the Hicks integrator have shown themselves to 
be valuable instruments for estimating the solar intensity, so far as 
transpiration is concerned. They should be suitable for the com- 
parison of light intensities in different habitats, etc., and they are 
especially to be recommended on account of their power of auto- 
matic integration, and also on account of the fact that they all give 
their results in terms of vaporization of a liquid, thus resembling 
the plant in its transpiration activity. The black bulb thermometer 
_ recommends itself as the best of the non-integrating devices. The 
photographic papers are not to be highly recommended as used 
in this inquiry, mainly on account of their failure to record effects 
of other than restricted wave-lengths. They may be modified so 
as to be more available, and may, possibly in their present form, 
be even more valuable than the other instruments here tested, when 
the effects of light variations on photosynthesis rather than trans- 
piration are to be determined. 
THE Jouns Hopkins UNIVERSITY 
BaLtmore, Mp. 
