916 
adjudged. A depositional equivalent has been 
found in a neighboring State. In central Arkan- 
sas, the unconformity is now discovered to be 
represented by no less than 20,000 feet of sedi- 
ments. The real values of the new relation- 
ships of the horizons are better shown by a 
rectified general geological section of the Car- 
boniferous of the region. 
WESTERN INTERIOR SECTION. 
Series. Terrane. | Thickness. 
Oklahoman. | Not here differentiated. | 1,500 
| Cottonwood limestone. 10 
Atchison shales. 500 
| Forbes limestones. 25 
| Platte shales. | 105 
| Plattsmouth limestones. | 30 
Missourian. | Lawrence shales. 265 
| Stanton limestones. | 39 
| Parkville shales. | 75 
| Iola limestone. 30 
Thayer shales. 50 
Bethany limestones. 75 
| Marais des Cygnes shales. 250 
Des Moines. | Henrietta limestones. 50 
| Cherokee shales. _ 200 
Arkansan. __| Not here differentiated. | 20,000 
Mississippian. | Not here differentiated. 1,500 
Of these five series of the Carboniferous sys- 
tem, the Oklahoman represents the so-called 
Permian; the next three the coal measures ; 
and the Mississippian the Lower Carboniferous, 
Measured in sediments, the horizon of the 
Thayer crinoids is far up in the Carboniferous, 
instead of being near the base. At Kansas City, 
where the crinoids were found, the Arkansan is 
represented by the hiatus—a period of vast 
erosion in that locality. 
CHARLES R, KEYES. 
THE PROCESS OF FREEZING IN PLANTS. 
In text-books on plant physiology, and in 
original articles upon the effects of freezing in 
plants, or on allied subjects, so far as is known to 
the writer, there is no working explanation of 
the process. The matter is referred to by Det- 
mer and Moor, Vines, Haberlandt, Sorauer, 
Sachs and many others, but without detailed 
explanation. 
The cells bounding the intercellular spaces 
(in leaves) are always moist on the side in con- 
SCIENCE. 
(N.S. Von. XIII. No. 336. 
tact with the air. As cooling goes on, all the 
tissue, contents of the cells and all, are con- 
tracting ; but when a temperature ofabout 4° C. 
is reached, the water content of the cell begins 
to expand, while the wall goes on contracting. 
This forces more moisture into the intercellular 
spaces. When the freezing point for water is 
reached, ice crystals begin to form outside of 
the cell in the intercellular spaces. The ice 
crystals will form first here, because water has a 
higher freezing point than the solution within 
the cell. As cooling goes on, and further crys- 
tallization takes place, the freezing water gives 
off its latent heat which tends to keep, for a 
considerable time, the cell contents from freez- 
ing. The crystallizing water without the cell 
extracts water from the cell by an inherent at- 
tractive force which the molecules of the mother 
crystal have for its liquid. This force is the 
cause of further water being drawn from the 
cell to build up the crystal of ice, and this at- 
tractive force is a similar one to that which 
causes plasmolysis in the case of the common 
experiment with cells of Spirogyra and a solu- 
tion of sodium chloride. The ice forms first in 
the intercellular spaces and continues to form 
there until the cell contents become frozen. 
If a leaf so frozen be subjected to a higher 
temperature, water will be formed in the inter- 
cellular spaces, resulting ina translucent, ‘ water- 
logged’ appearance of the tissue of the leaf. 
If, however, the temperature be raised very 
eradually, the cells will probably resorb the ex- 
tracted water as rapidly as it is formed, result- - 
ing in no permanent injury to the leaf. Sachs 
found that the leaves of the beet and the cab- 
bage frozen at from — 4° C. to — 6° C., and 
thawed in air at 2 to 8° C., were killed, while 
when thawed slowly in water at 0° C. they sur- 
vived. 
If the temperature be low enough and be con- 
tinued long enough a permanent injury would 
result, for then the cell-contents would become 
solidified. 
In the case of the experiment with a beet 
partially scooped out and subjected to a freez- 
ing temperature, the formation of ice in the 
cavity is brought about in exactly the same way 
as it is in the intercellular spaces in leaves of 
plants, excepting on a larger scale. If the 
