86 
Proceedings of the Royal Society of Edinburgh. [Sess. 
In his monograph Sachs gives hourly and three-hourly statistics of 
twelve experiments on shoots, green as well as etiolated, some of limited, 
others of unlimited growth. These observations extended over periods 
varying from four to twelve days, and were carried on during the months 
of April, May, and June. Each experiment was worked for a fixed twelve- 
hours day and twelve-hours night, irrespective of the length of day and 
night to which under natural conditions the plant would have been exposed 
at the time of experimentation. 
Baranetzsky improved on Sachs’ apparatus, confirmed the main points 
of the latter’s research, and generally extended our knowledge of the daily 
periodicity. His monograph contains statistics of thirty-five experiments 
under more varied conditions than those of Sachs. The majority of these 
consist of observations on Gesneria tubiflora and Gesneria cardinalis, 
the remainder on green and etiolated shoots of Heliantlius tuberosus, and 
etiolated Brassica rapa. His periods of observation are short, varying 
from two to six days, and only in few instances extended to seven, nine, or 
ten. Presumably the optimum temperature for each plant species under 
observation was determined, and the temperature during experimentation 
kept below the optimum : the same species in different experiments is 
subjected to temperatures varying from 21° to 29° C., and in some cases in the 
same experiment a variation of temperature of 2° to 4° is scheduled. The 
experiments were carried on during the months of April, May, June, and 
July, and for uniform day and night periods of twelve hours similarly to 
those of Sachs. 
While Sachs was of opinion that an autonomic variation underlay the 
daily periodicity, Baranetzsky considered the latter an induced phenomenon. 
He found that it disappeared in three days in shoots of Gesneria tubiflora 
kept in continuous darkness, and in Helianthus tuberosus after a some- 
what longer period (fourteen days), being succeeded in each case by 
irregular variations of varying amplitude. Further, in etiolated shoots of 
the latter grown from the tuber in darkness, the daily periodicity was 
not manifested. On the other hand, in shoots of Brassica rapa, pro- 
duced from the tuber in darkness, a periodicity of growth similar to 
the daily one was found. This Sachs regarded as evidence for the 
autonomic nature of the variations, while Baranetzsky regarded it as 
a phenomenon of correlation, where the tendency to periodicity was 
transferred as an after-effect from the tuber to the stem. On the other 
hand, this might be explained as an inherited tendency to periodicity 
in the organ. 
Pfeffer is of opinion that heredity does not enter into this question. 
