682 TRANSACTIONS OF SECTION K. 
These results, however, were only obtained when the times were short 
(? not greater than the presentation time). If the summation of the individual 
times in the two directions (7 and ¢) is greater than about fifteen minutes, it is 
found that the larger force has less effect than would be calculated from the 
above equation, and the radicles must be exposed to the force for a longer time 
in proportion to the period at rest, i.e., C7 >gt when a result without any 
ultimate bend is obtained. 
Most of the work has been carried on with the radicles of Helianthus annuus 
and Cucurbita Peyo about 4 to 14 cm. long. 
7. Thermotozry, or Factors in the Growth of Cotton in Egypt. 
By W. Lawrence Batts. 
Investigations of the growth of a fungus-hypha, with temperature as the 
limiting factor,’ showed that growth accelerated according to chemical laws with 
rise of temperature up to 374° C., when it was rapidly arrested. The position of 
the so-called optimum was determined by the rate of heating. This arrest was 
due to the formation and excretion of a toxic. katabolite, and the ‘ stopping- 
temperature’ could be fixed at any desired point from 15° C. to 374° C. by using 
various concentrations of this stale culture-medium mixed with fresh medium or 
with water. The excretion accelerated more rapidly than the growth-rate as the 
temperature rose, and so neutralised it. The toxin itself was not isolated pure, 
but it could be decomposed in vitro, or removed from stale cells by washing or 
by desiccation and storage. 
Similar interpretations are indicated by the higher plants. In their case the 
removal must be due to decomposition—probably oxidation. The effect is 
clearly shown by Egyptian cotton under field conditions, since the growth takes 
place chiefly during the night, the water-strain brought about by high sun- 
temperature and low humidity preventing growth in sunshine during a great part 
of the growing season. Growth therefore follows the night-temperature as a 
rule, but when the day-temperature has exceeded 35° C. we find the growth during 
the following night to be subnormal, limited by the accumulated toxin. If a 
ert: day follows, the toxin is decomposed and the next night’s growth is 
normal. 
Continued repetition of such over-heating results in complete arrest of growth 
in the affected bud. Different races and species of Gossypium differ in their 
liability to this poisoning under the same conditions, without any relation to 
their temperature-acceleration of growth. Hybrids therefore show most various 
growth-relationships in F2., e.g., slow but continuous, rapid but discontinuous, 
&c., and there are indications that a Mendelian segregation may be found. 
Such over-heating may be caused if the plant is short of water, although the 
shade air-temperature does not exceed 35° C., since closure of the stomata results 
in partial loss of thermo-regulation, and in a rise of tissue-temperature above air 
temperature even to 10° C. Simple water-shortage needs to be differentiated 
carefully from the heat-poisoning which it may entail in hot climates. The effect 
of root-asphyxiation by a rise of the water-table acts partly in this way. 
The growth-temperature curve of the root in non-aerated water-culture suggests 
a similar toxic accumulation as the result of a limited air-supply. The general 
conception of toxic katabolites accumulating too rapidly, or being too slowly 
decomposed, seems to be useful; direct chemical investigation should be feasible, 
as in the analogous case of muscular fatigue. 
There is a hint of a wider generalisation in the hypothesis of Thermotoxy— 
namely, the possibility of antagonising this effect by an antitoxin, both in plants 
and in animals. White men in the tropics are exposed to supernormal tempera- 
tures for long periods, and the intermittent breakdown of their thermo-regulation 
is shown by the greater frequency of low fevers and slight rises in temperature 
due to extraneous causes, as compared with the same in Europe. An anti-thermic 
serum, were it possible, supplementing present precautions against sunstroke, 
malaria, and so forth, would enable the white races not merely to occupy, but to 
colonise the Tropics. 
* Ann. Bot., 1908. 
