SAP DENSITY AND FREEZING POINTS OF LEAVES. 103 
1. NOTES ON THE EFFECT OF THE FREEZE OF APRIL 24, 
1910, ON THE TREES AND SHRUBS GROWING IN THE MIS- 
SOURI BOTANICAL GARDEN, THEIR RECOVERY AND OTHER 
DATA. 
The continental position of Saint Louis is such, that it 
is practically unaffected by the proximity of large bodies 
of water or mountain ranges. It lies in a large river valley 
about midway between the divides of the Appalachian and 
Rocky Mountain ranges. In every direction the country 
is open for hundreds of miles, except as it is interrupted 
by the retaining walls of the two mountain ranges already 
referred to. To the south lies the Gulf of Mexico, and 
it is, as might be expected, one of the storm-forming areas 
of this section. The storms from this section are in the 
main warm, and although often destructive, need not be 
considered in connection with this paper. To the north 
the storm area is more varied, and the storms that sweep 
down from this section are usually very cold, and often 
very sudden. Since east and west need not be taken into 
consideration as affecting temperature changes directly, 
they may indirectly be responsible for subjecting Saint 
Louis to the extremes of temperature from the north and 
south, 7. e., they form the channel through which these 
winds are forced to blow. Since it is unaffected by the 
tempering influence of large bodies of water, its frost period 
is much later than that of cities of corresponding latitude 
on the oceans, or near them. (Dorschied, Metr. Zeitschr. 
24: 11-24. f. 7.; 49-64. pl. 7. 1907.) Dorschied places 
Saint Louis on the same line, as regards beginning, ending 
and mean duration of frosts, as points on the coast of Alaska, 
British Columbia, New England, Southern Iceland, Nor- 
way, and the Western Alpine and Mediterranean regions. 
The average date of the last killing frost for Saint Louis 
is April 2. (Garriott, E. B. Notes on Frost. Farmers’ 
Bull. U. S. Dept. Agr. 104:16. 1910.) The prevailing 
direction of the wind during the month of March, 1910, was 
from the southwest, and means that this was a warmer 
month than usual. Quoting the summaries for March and 
