22 BULLETIN 193 



The writer has under observation one-year-old seedling trees of 

 white pine which grew in the summers of 1914 and 1915 under large 

 cheesecloth shades which reduces the light approximately to the values 

 shown in tables XIII and XIV. One set was transplanted to give each 

 tree space for the development of its root system; the other set was 

 left as they came up after broadcast sowing. 



A comparison of the size, color and general vigor of the two sets 

 seems to indicate beyond a doubt that the chief factor of the slow 

 development of the latter set is not lack of light but some other factor, 

 possibly root competition for water and food in the soil. 1 



i 



CONCLUSIONS 



1. The word "tolerance" should be stricken from the vocabulary 

 of forestry students unless to it can be accorded a more comprehensive 

 definition. It is taken generally to express a light relationship, but 

 really it expresses not a light relationship, but the total relationship of 

 a tree to all factors of the habitat. 



2. The filtered light in the forest has little value as a means of 

 decomposition of carbon dioxid; the important light in the forest is 

 weakened white light. 



3. Light intensity data thus far published in forest light studies 

 as a rule are averages of many readings, usually taken without refer- 

 ence to check readings in the open. They have been taken commonly 

 on clear days about noontime and consequently readings usually are too 

 high. Furthermore, the fact that shade in the forest is discontinuous 

 is additional evidence of the untrustworthiness of much of the pub- 

 lished data. 



4. The relation of tree growth to light as an influencing factor 

 can be determined only by controlled greenhouses and nursery trials. 

 Light readings in the forest are of little value. 



ir The writer is well aware of the fact that these cheesecloth shades have a de- 

 cided influence upon all factors of this artificial habitat. Continuous records of 

 changes in humidity, air and soil temperatures were taken during the season. 

 Rainfall, soil moisture, and evaporation data were also collected. These figures 

 will be published after further experimental data are available. 



