64 



THE PLANT WORLD 



shrubs at the top. The best one of several places observed was the cut 

 on the Laurel trolley road between Langdon and the Queens Chapel 

 Road. Here the cut is quite steep, and along the top there is a consider- 

 able amount of shrubbery. The edge has a slightly overhanging position 

 so that any body or object falling from these would strike the slope at 

 nearly its steepest point. The snow falling from the shrubbery striking 



Figs. 1-4. — Frost-weed ice wings, reduced one-fourth. Fig. 4 is side view from point a 

 of Fig. 3. 



Fig. 5. — Diagrammatic sketch showing formation of snow rolls on January 10. a, Sec- 

 tion of roll, the center being the mass of snow which fell from vegetation at A. 



upon the steep part of the slope immediately below, adhered to the snow 

 on the slope, and by its momentum started to roll down the side of the 

 cut. The snow had melted just enough to make the formation of snow- 

 balls easy, and as the ball started to roll down the slope the snow adhered 

 together and rolled up very much on the principle of cotton batting. As 

 the rolling mass was small at first, however, the actual shape assumed 

 was very closely that of a snail shell. Helix, the more so as the snow 



