TEACHERS DEPARTMENT. 
45 
Distribution on uplands along swamp borders is also deter¬ 
mined in part by the nearness of the underground water level to 
the surface. The classification of vegetation as upland or low¬ 
land depends upon this factor. Local distribution of the vegeta¬ 
tion is subject also to physiographic control. 
In connection with this paper may be mentioned the conclusions 
of Whitney and Cameron (U. S. Dept. Agri., Bureau of Soils, 
Bull. 22, 1903) that, “ there is no obvious relation between the 
amount of the several nutritive elements in the soil and the yield 
of crops/’ but that, “ the actual quantity of water a soil can 
furnish a plant, irrespective of the percentage of water actually 
present in the soil, has probably a very important influence on the 
yield.” 
This supply of water to the plant would depend upon the 
coarseness or fineness of the soil, as has been shown experiment¬ 
ally by Livingston and Jensen (Bot. Gaz. 38: 67. 1904). 
C S. G. 
The Protection of Winter Buds. —A very common miscon¬ 
ception has gained currency concerning the purpose of certain 
structures in winter buds. It is very pretty poetry to speak of 
the “ baby plant, snugly wrapped in its warm blanket to keep it 
fi om freezing ”! but any one may readily demonstrate the fallacy 
of the idea on any winter’s day when the temperature is below 
freezing. If horse-chestnut or other buds are cut open on such 
a day they will be found packed with ice and the bud itself 
frozen. Evidently the “ warm blanket ” must serve some other 
purpose than the prevention of freezing. What is this purpose? 
It is a well-known fact that frozen plants may frequently be 
saved by allowing them to thaw while immersed in water. Loss 
of turgor does not then take place and the freezing is not fatal. 
Similar factors are involved in the ecology of winter buds. When 
a cell is reduced to the freezing temperature water leaves the cell 
and solidifies in ice crystals outside the cell wall. If the cell or 
cellular tissue is freely exposed to the air the water evaporates 
when a rise of temperature melts the ice. Plasmolysis thus be¬ 
comes permanent and the frozen tissue dies. The protection 
afforded by the bud coverings prevents evaporation when the ice 
