438 BOTANICAL GAZETTE | [ DECEMBER 
tion of one plant, that the slow thawing does not restore to activity. The 
sole exception was that of excised leaves of Agave Americana. If these 
were frozen in a not too low temperature, slow thawing restored more cells to 
activity than did rapidthawing. Géppert’s work in using the change in color 
in the indican-holding blossoms of orchids as a test for the death of the pro- 
toplasm, was imitated by Molisch in using three marine Floridezx, Nito- 
phyllum, Gelidium and Plocamium, red algze which become orange on dying. 
In this test thg orange color always came when the plants froze. The author 
had previously found that the plant Ageratum Mexicanum exhaled the odor 
of cumarin on dying. He therefore used this plant also as a test, and found 
the cumarin odor appearing when the plant froze. To the reviewer this 
work on the Floridez and Ageratum seems the most important part of the 
whole paper. 
The injury to plants by temperature just above o° was also studied. 
Molisch concludes, as others have before him, that in many cases the injury 
is due to excess of transpiration over absorption of water. In other cases the 
injury cannot be due to this cause, for it takes place when transpiration is 
checked by external means. Molisch believes that the injury in such cases 1s 
due to a disturbance of the metabolism of the organism, and suggests that 
there may result the accumulation of some toxic product, or a failure in the 
production of some necessary substance. Many plants, all from warm cli- 
mates, were used in obtaining this result. A plant especially sensitive was 
Episcia bicolor, whose leaves became brown and contained mostly dead cells 
after an exposure of four days to a temperature of 3°. Preventing transpira- 
tion, shielding from the light, very gradually changing from a warm toa cold 
temperature, made no difference. Nearly all the species of plants used died 
within thirty-five days; a few lived two and one-half months; while two plants 
of Philodendron pertusum lived through the winter in the cold, but suddenly 
died in the first warm days in March. 
Lastly, Molisch comes to the theory of death by freezing. Death comes 
with freezing, not with thawing, and is due to the withdrawal of water from 
the protoplasm. Thus Molisch finds himself in complete accord with Miiller- 
Thurgau, who has given us a like explanation. The reviewer is not dispose 
to object to this conclusion in a general way, but would suggest that there - 
are various phenomena, some of which are mentioned in the present pape? 
that do not come into harmony with the theory. To mention one of these '§ 
enough: Miiller-Thurgau has found, and Molisch accepts the result, that the 
more the temperature is lowered, the more is the ice formed, and conse 
quently the more is the water withdrawn from the protoplasm. Molisch 
states that wilted plants are less likely to be injured by frost than not wilted. 
This query, of course, comes: Why, according to the theory of injury he! 
freezing, should not a given low temperature leave as much water in the 
protoplasm of a turgid plant asin that of a wilted plant ?—F. C. NEWCOMBE: — 
