PLATE 21 



A. — Chilled and unchilled plants of grouseberry, Viburnum americanum. The 

 illustration shows two i-year-old seedlings with the same history', except that the one 

 at the right was kept during the winter in a warm greenhouse at a temperature of 55 

 to 70 F., while the one at the left was wintered in a cold greenhouse at a temperature 

 of 32 to 40 . When spring temperatures warmed up this coldhouse, the plants in it 

 began to grow, and on April 7, 1914, when the photograph was taken, they had reached 

 the stage shown in the left-hand figure , while the plants in the warmhouse , as illustrated 

 by the right-hand figure, were still completely dormant. 



B. — Chilled and unchilled plants of tamarack, Larix laricina. These two seedlings, 

 grown from seed procured in Alaska, have had the same history except that the one at 

 the left was wintered in a cold greenhouse at a temperature of 32 ° to 40 F., the one at 

 the right in a warm greenhouse at a temperature of 55 to 70 . When the photograph 

 was taken, on April 10, 1914, the chilled plant had put out new growth in the warm 

 spring weather, while the unchilled plant still showed only its leaves of the year before. 



