RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 47 
fatal effects when the minimum light has been exceeded. For ex- 
ample, if seedlings of a given species are grown with 20, 40, 60, 80, 
and 100 per cent of the full available light, other conditions being 
equal, and if the greatest accretion is put on by those having 60 and 
80 per cent, while those having only 20 per cent barely exist, and 
some of their number succumb, it will be fairly evident that the 
optimum is between 60 and 80 per cent, and the minimum slightly 
below 20 per cent for the given conditions of heat and moisture. 
Both points may be found quite closely enough by curving the 
growth data. Similarly, in other temperature and moisture series 
different optima and minima of light may be found, and the abso- 
lute optimum combination may be very nearly arrived at. 
On account of the difficulty of duplicating any set of conditions 
at different periods, it is extremely desirable that the more im- 
portant species whose relative tolerance it is desired to know should 
all be treated during the same period, and also that an arrangement 
should be effected which will make possible different combinations 
of light with moisture and temperature. 
The following plan for such experimental determination of toler- 
ance, while merely suggestive, may assist in initiating some work 
along this very important line. The arrangements suggested should 
accommodate about four species. It would, perhaps, be well to run 
an initial test with rather gross differences in the light quantities, 
as suggested above, and to repeat at a later date when the knowl- 
edge obtained will permit more minute examination of the critical 
points : 
Construct a solarium about 5-| by 8 feet, with its long axis lying 
east and west, its floor and glass roof having possibly a gentle slope 
to the south. The depth from glass to floor need not exceed 18 
inches. Divide this into three equal parts by means of glass parti- 
tions running north and south. If two layers of glass are used 
throughout, having dead air between them, the purposes will be 
more completely fulfilled without affecting light quantities appre- 
ciably more than would the single layer of glass. Let the higher 
north wall serve as entrance to the compartments, being closed by 
a door whose inner surface has very poor reflecting powers. 
For each of these compartments 10 pans, each a foot square and 6 
inches or a foot deep, will be required. These may be made of gal- 
vanized iron with drainage openings in the bottom. Into each pan 
put a measured quantity of soil, sufficient to fill it to within 2 inches 
of the top. The pan and dry soil weight both having been deter- 
mined, the amount of water necessary to maintain a given moisture 
percentage in the soil may easily be computed, and this, added to 
the gross dry weight, will give the weight which the pan should 
show after each watering. 
Each pan may now be sown with sufficient seeds of the several 
species involved to produce a good stand on the area of 1 square 
foot. Possibly 100 seeds of each species should be used in each, the 
