the case 23 Potamoseton, beepden 10° and 1 Se OSS Valliheae: abow 
cis 210 ae aS tructural Pay 4 Physiological Botany. a 
6° C. hie 
The sensitiveness and periodical movements of the leaves af the 
"sensitive plant do not begin till the temperature of the surrounding air < 
. exceeds 15° C. ; the rapid periodical movements of the lateral leaflets < 
iof the leaf of Disses gyrans only at a temperature above 22° C. 
The action of higher temperatures on 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 50° C. ina few minutes, but may again become sensitive when the ~ 
temperature falls. A temperature of 52° C. causes permanent loss of 
motility and death. 
The lower limit of temperature for the motility of the protoplasm , 
in Witella syncarpa is zero ; for the hairs of the pumpkin Io~ to 11° C, 
_ The upper limit is 37° C. in the former case ; in the latter the current is 
arrested within two minutes when immersed in water of 46° or 47° C. ; 
in water above that temperature within a minute ; in the air, exposure 
to a temperature of 49° or 50° C. for ten minutes does not stop the 
current. 
The absorption of water through the roots is also sub‘ect to certain 
limits of temperature. The roots of the tobacco and pumpkin, for 
example, do not absorb sufficient water in a moist soil of from 3° to 5° 
C. to replace the small loss caused by evaporation, the leaves hanging | 
in a flaccid condition in consequence of the cessation of their turgidity. 
The rapidity and intensity of the vital functions are not in proportion 
to the increase of temperature. The rate of growth of the roots of a seed- 
ling of maize attains its maximum at 27°-2 C. ; of the pea, wheat, and 
barley at 22°°8 C. The sensitiveness of the leaves of AZimosa reaches 
its maximum at 30° C.; the rapidity of the movement of the protoplasm ~ | 
in Nitella syncarpa at 37° C. 
If the limits of temperature mentioned above are passed, 
the vital functions of the plant may simply come to rest, 
as is the case with perennial plants during the winter season; 
or permanent changes are brought about in the plant or in 
parts of it, resulting in injury or death. The fatal injury in- ee 
flicted on cells, both by too high a temperature and by 
freezing, is a consequence of their containing water. = 
Air-dry peas can resist a temperature of over 70° C. for above an 
hour without losing their power of germination ; soaked in water for rs | 
an hour and exposed to a temperature of 53° or 54° C., they are 
