RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 47 



the minimum light has been exceeded. For example, if seedlings of a 

 given species are grown with 20, 40, 60, 80, and LOO per cenl 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 tho$ 

 having only 20 per cent barely exist, and some of their number suc- 

 cumb, it will be fairly evident that the optimum is between 60 and 80 

 per cent and the minimum slightly below 20 per cenl 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 absolute 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 nunc important 

 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 combination- of light 

 with moisture and temperature. 



The following plan for such experimental determination of toler- 

 ance, while merely suggestive, may assist in initiating stum' 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 quant it i 

 as suggested above, and to repeat at a later date when the knowledj 

 obtained will permit more minute examination of the critical points: 



Construct a solarium about 5^ by 8 feet, with its long axis Iving 

 east and west, its floor and glass roof having possibly a gentle -l<>p<- 

 to the south. The depth from glass to floor need not r\. •,.,<! 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 appreciably 

 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 <» 

 inches or a foot deep, will be required. These may be made ol gal- 

 vanized iron with drainage openings in the bottom. Into each pan 

 put a measured quantity of soil, sufficient to hi it to within ., 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 sho* 



after each watering. . , , i 



Each pan may now be sown with sufficient seeds oi the several 

 species involved to produce a good stand on the area o 1 square 

 foot. Possibly 100 seeds of each species should he used in ea< Ik tn< 



