UNITED STATES DEPARTMENT OF AGRICULTURE 
BUREAU OF BIOLOGICAL SURVEY 
IN REPLY REFER TO     S0RRS, CONNETCTIJT 
April 24, 1936 
Prof. !ldo Leopold 
University of Wisconsin 
adison, aIisconsin 
Dear Leopold: 
The last few weeks have been busy with planting of trees and shrubs 
on our demonstration area so have delayed answering your letter of April

3. 
The work that I did on yields of weeds was published last year in 
AGmerican O'me in the article on 2arrying Capacity. I did have some 
scattered inforration on yield of fruits but with the limited time 
at  iillimston, I stressed the wild seeds rather than the fruits. In 
order to obtain a satisfactory sample of say frost grape, one would have

to pick every grape in a whole section, so scattered are the vines. I 
didn't have the time or would have attempted something of the sort for 
frost grape, pmanicled dogwood, red berried nightshade, Crataegus and 
others. 1 hope some of your students may tackle something of this na- 
ture. 
Mere in Connecticut, tIe skunk cabbage is very -bundant, but as to 
yield, I haven't the slightest idea, so in connection ,,ith our demons- 
tra ion area we are going to sample the yield. 
The rabbit problem is coiling along. iaterial is not too abundant 
and ahen the subject studied is nocturncl end crepuscular in its habits 
it keeps one on the job when the fanily wants to eat supper! ,4e are 
workino on a self-recording7 device by which the rabbit will write its 
own record of acti ity - to and from forms, burrows, nests, etc. Light 
seer s to be a vital factor in regulatin' the time of beginning activity.

At the college here, Dr. Viallace, a plant physiolo gist has developed a%

self recording potentiometer giving continuous light records. I con- 
sider this instrument the best  f its kind in the United Jtates.  e 
are plmnning to use one of these instruments. There are about a dozen 
now in existence. 2he blueprints can be obtained from Dr. R. H.  1allace

for one dollar. 
This instrument places the recording of light values on a par with 
thermographs, hygrographs and the like.