66 rk BOTANICAL GAZETTE [JULY 
coefficient of the duration of life of Tubularia crocea stems was of 
the same order of magnitude as that found by Loes for sea urchin 
eggs, being about 2 for each degree centigrade rise in temperature. 
The results of these investigations on animals led GooDSPEED (3) 
to determine the temperature coefficient of the duration of life in 
barley, which was found to be 1.27 for an interval of 1° C., or 
about 11 for 10° C. This result is much lower than that found by 
Logs for sea urchin eggs, and by Moore for hydroid stems, and 
is much higher than the temperature coefficients determined for 
growth phenomena in plants. 
The results obtained with barley involved the use of relatively’ 
high temperatures, and it was suggested to me that similar investi- 
gations upon the marine algae, involving a lower range of tem- 
perature, might yield data which could more properly be compared 
with the results obtained with simple animal organisms by LOEB, 
Moore, and others. Another reason for using an alga is that 
we then deal with a much simpler structure than was used by 
GoopsPEED (loc. cit.), thus eliminating to a certain extent the 
possibility of unknown factors entering into the experiment. 
Physiologists have recognized that the degree to which van’t 
Hoff’s rule applies to physiological processes is determined by the 
degree of uniformity in which experimental material is affected 
by the environmental changes. Thus, whenever it is possible, 
isolated cells are chosen for experimental purposes, a small energy 
change being the most influential cause of uniformity in physio- 
logical reactions (cf. BARRY 1). In this connection it is to be 
noticed that the tissues used for observation in the present experi- 
ment were those in the apical region, and were thus embryonic in 
character; hence, the following observations are more nearly 
comparable with those of other investigators who have used 
embryonic animal cells or tissue in their investigations. 
Of the material available, certain members of the Rhodophy- 
ceae were chosen, especially those species which are known to show 
a more or less definite death point by a rapid and distinct change 
of color. In a number of preliminary experiments the plant which 
passes commonly as the Pacific Coast form of Ceramium tenuts- 
simum gave the sharpest death point color reaction, and for this 
reason was used exclusively. : 
