398 BOTANICAL GAZETTE [December 



covered with a less plastic seal of about equal parts of the two 

 ingredients. Little difficulty was experienced in keeping a perfect 

 seal intact. 



The broad-leaved trees, Acer saccharinum L., Ulmus americana 

 L., and Quercus macrocarpa Michx., were handled in identically the 

 same manner as the preceding, except that they were grown from 

 seed sowed in flats in the greenhouse, but the plants were trans- 

 ferred to pots out of doors in June. 



In order to insure uniform soil temperature conditions for all 

 plants concerned, and changes of temperature similar to those under 



Fig. I. — Arrangement of trees in containers, with collars to insure temperature 

 changes comparable with those of plants growing under natural conditions. 



natural conditions, the containers (approximately 100 in number) 

 were placed in tin cylindrical collars, each collar being slightly 

 larger than its respective container. These were in rows about 

 6-10 inches apart and completely surrounded by soil. The top of 

 each container and collar was covered with a heavy woolen blanket, 

 slit to accommodate the stem, and this in turn with a piece of thick 

 muslin waterproofed by infiltration with the hot wax seal mixture. 

 The edges especially, and also the whole cloth, as well as the sur- 

 rounding soil, were covered with a thin layer of sand. To prevent 

 the drifting of snow among the trees thus planted on the University 

 campus, the collars and inclosed containers were set on the bare 

 soil surface, and the well-tamped soil filled in between them was 

 held in place by a board frame 12 inches high (fig. i.) 



