INFLUENCE OF TEMPERATURE ON VEGETATION. 
729 
in Phaseolus multiflorus and Zea Mais at 9-4° C. ; in Cucurbita Pepo at i3-7°C. But 
when the reserve-materials of the seed have been consumed, a higher temperature is 
apparently always necessary to enable growth to proceed at the expense of freshly 
assimilated material. The highest temperatures at which my observations indicate 
that germination can take place were about 42° C. in the case of Phaseolus viultiflorus^ 
Zea Mais, and Cucurbita Pepo ; in Wheat, Barley, and Peas, about 37° or 38° C. 
The lowest temperature at which the chlorophyll- granules turn green was 
determined for Phaseolus multiflorus and Zea Mais at above 6°, and probably 
below i5°C.; for Brassica Napus above 6°C. ; for Pinus pinea between 7° and 
ii°C. The highest temperature at which leaves already formed and still yellow 
turn green was for the first-named plants above 33° ; for Allium Cepa above 36° C. 
The exhalation of oxygen and the corresponding assimilation begin, according 
to Cloez and Gratiolet, in the case of Potamogeton between 10° and i5°C. ; in 
Vallisneria above 6° C. In many Mosses, Algae, and Lichens, assimilation may 
possibly take place at still lower temperatures ; according to Boussingault (Compt. 
Rend. vol. 68. p. 410), carbon dioxide is decomposed by the leaves of the Larch 
at 0-5° to 2-5° C, and by those of Meadow-grasses at 1-5° to 3-5° C. Heinrich 
found the minimum temperature at which bubbles of gas were given off by Hottonia 
palustris to be 2-7° C. The upper limit of temperature for this function has not 
been ascertained, except for Hottonia palustris^ in which case Heinrich found it 
to be 5o"-56"C. 
The irritability and periodical movement of the leaves of Mimosa do not 
begin till the temperature of the surrounding air exceeds i5°C. ; the periodical 
movements of the lateral leaflets of the leaf of Desrnodium gyrans only at tem- 
peratures above 2 2°C. The upper limit of temperature for the sensitiveness of the 
leaves of Mimosa depends on the continuance of the warmth ; in air of 40° C. 
they become rigid within an hour; at 45° C. within half an hour; at 48° to 50° 
within a few minutes, but may again become sensitive when the temperature falls. 
A temperature of 52° C. causes permanent loss of the power of motion and death. 
The lower limit of temperature for the motility of the protoplasm in Nitella 
syncarpa is stated by Nägeli to be zero ; for the hairs of Cucurbita my observations 
place it at a temperature of 10° or ii°C. The upper limit is 37° C. in the case of 
Nitella syncarpa according to Nägeli ; in the hairs of Cucurbita, when immersed in 
water of 46° or 47° C, the current is arrested within two minutes; in the air exposure 
to a temperature of 49° or 50° C. for ten minutes does not stop the current. The 
current in the hairs on the filaments of Tradescantia ceases within three minutes in air 
at 49° C, beginning again when the temperature is reduced. 
The absorption of water through the roots is also confined to certain limits of 
temperature. Thus I found that the roots of the Tobacco-plant and Gourd no longer 
absorb sufficient water to replace a small loss by evaporation in a moist soil of 
from 3° to 5°C. ; the heating of the soil to from 12° to i8°C. suffices to raise 
their activity to the needful extent. The roots of the Turnip and Cabbage on the 
contrary absorb a sufficient quantity of water from soil reduced nearly to the free.zing- 
point to replace a moderate loss by transpiration. 
A second result of the observations hitherto made may be stated as follows : — • 
The functions of a plant are assisted and accelerated in their intensity when the 
