226 TWENTY-FIRST REPORT. 



extract might best be carried out in vacuo, but sufficient apparatus was not 

 available. 



Precipitation was carried out very carefully — all vessels having been 

 weighed and microscopically inspected for traces of resin and all acidulated 

 wash water was tested for traces of resin to see if any was lost. Fortunately, 

 a means was at hand for controlling to a nicety the temperature, which is 

 such an important matter in the precipitation of this resin. This was carried 

 out in the intermediate room of the dairy refrigerator, whose temperature 

 (10° C.) remained invariable during cold and warm weather. The precipitated 

 resin was dried at 95° C. for a few minutes, then raised to 98° C. and held 

 at this point for a half hour till a fairly constant weight was obtained. 



HABITATS AND CHARACTERISTICS OF COLONIES SELECTED. 



The first colony designated by 1 a and 1 b in Series I and II of the follow- 

 ing tables was located on a 15° slope and received direct sunlight till noon, 

 and diffuse light (thin shade of white oak) for two hours longer. It is in 

 an exposed place with constant air currents and slight crowding by herbs and 

 trees. The second colony, 2 a and 2 b of Series I and II of the tables, was 

 on a steeper slope (25-30°), with fewer trees of the same species (white oak 

 and hickory) as those of colony one. These formed a thin shade for only 

 short periods throughout the day. Crowding by other plants, e. g., herbs and 

 trees, was absent, while in number one this may have been a growth factor. 



Colony three, 3 a and 3 b of Series I and II in table, was about 60 feet 

 lower than the above two, but air movement was not as great as in colony two, 

 which in turn is exceeded by colony one in this respect. The slope of the soil 

 in this colony was like that of colony two, but the hun^idity was doubtless much 

 greater on account of more dense forest of considerable extent in all directions. 

 From the work of Gleason and Gates,^ one may infer a lower transpiration, 

 which could perhaps constitute an important factor in the limited growth of 

 this colony referred to below. 



Colony three had a diffuse light angle of 30° and a dense shade angle of 

 60°, the hills on the east and west cutting off the sun completely during the 

 rest of the day. These angles were accurately measured and the total amounts 

 of light energy received by the different colonies were calculated. 



On an absolute scale, colony one received approximately 60 per cent of 

 the full amount of light energy possible In that latitude and altitude ; colony 

 two received about 85 per cent, and colony three less than 35 per cent. This 

 may not be an accurate measure of amounts of light used since in colonies 

 one and two, more light may have been furnished during the unshaded hours 

 than the plants could use, so that the ratios of amounts of light used in meta- 

 bolism are undoubtedly not so wide as the above percentage would indicate. 



The rhizomes were carefully dug. washed and dried with about three 



>Gleason, H. A., and Gates, F. C. A Comparison of the Rates of Evaporation in 

 Certain Associations in Central Illinois. Bot. Gaz. 53 :491, June 1912. 



