July 7, 1923 
Temperature Effects in Plant Metabolism 
23 
As regards the yield of dry matter, when allowance is made for the 
loss of one plant at the lower temperature it is apparent that this factor 
was virtually constant at the different temperatures. That such cor¬ 
rection should not be proportionate to the loss of plants in proportion 
to soil space is indicated by the work of Stewart (37). It should be noted 
that the discrepancy in numbers of seeds will be greatly reduced when 
one adds to those matured others involved in immature broken por¬ 
tions of the cultures. As the data stand, the weight per seed was some¬ 
what greater at the lower temperature. In view of the conditions just 
mentioned, this difference can hardly be considered important, because 
of the lessened competition for nutrients as compared with the cultures 
bearing more mature seeds. 
The plants grown at the lower temperature had a higher percentage 
of dry matter than the others, especially in the stems. The ether ex¬ 
tract was more abundant percentagely in the leaves of plants grown at 
the higher temperature. This agrees with the deeper green color devel¬ 
oped in this case, and is indicative of a relatively high chlorophyll con¬ 
tent. The difference extended to the stems to a lesser degree, but dis¬ 
appeared in the seed, where the extract would be limited largely to true 
fats. A determination of the iodin numbers of the two fatty extracts 
of the seeds gave 55 per cent for the higher temperature cultures and 
39.6 per cent for the others. However, the amount of material for 
analysis was too small to permit placing of emphasis upon these results. 
Polysaccharids were more abundant throughout the plant in the cul¬ 
tures grown at the lower temperature, but the difference was somewhat 
less with the leaves than other tissues. In this connection, the work of 
Spoehr (36) should be noted. He found that with the approach of the 
dry season the cactus increased in pentosan content. The change was 
ascribed to a regulative mechanism for retention of water through pro¬ 
duction of polysaccharids of high capacity for hydration. Spoehr also 
concluded that a relatively high temperature (28° C.) produced the same 
effect, but his data are not so convincing as in the case of humidity 
effects. In an investigation of frozen peppermint Rabak (30) found 
evidence of increased esterification of menthol. A similar result was 
obtained by drying the plant tissue. Here, an extreme removal of 
water from liquid condition in the plant cells seems to have caused rever¬ 
sion of the familiar enzymic process of hydrolysis. It may well be 
questioned whether a similar effect would be likely to occur at tempera¬ 
tures much above freezing, but by hardening treatment with tempera¬ 
tures approaching freezing, Rosa ( 33 ) induced an increase of pentosan 
in certain plants. 
It appears possible that the increase of polysaccharids observed in 
plants exposed to low temperature may bear some relation to disturbed 
equilibrium in the hydrolysis of these compounds. There are other 
possibilities, however, which should not be overlooked. One of these 
is the possible difference in net temperature coefficients for the synthesis 
of polysaccharids and of proteins in the plant. Another, and one rather 
more plausible than the others, is the possibility of limitation of poly- 
saccharid storage due to consumption of sugars by increased respiration 
at higher temperatures. In this case the tissues would be expected to 
become richer in nitrogen, as is found by analysis. 
With the exception of the seed, the nitrogen content of the several 
tissues of these buckwheat plants varied inversely as the polysaccharid 
content, but, even when expressed as equivalents of protein, they do 
