440 W. E. RITTER AND M. E. JOHNSON 
protozoon division, and of all cell division will have to be 
examined much more systematically and vastly more exactly, 
quantitatively, than they yet have been. 
3. The inadequacy of treating periodicity generally, as an 
aspect of fluctuating variation 
Here seems to be the place to point out how much more ob- 
jective, more workable, more important ‘periodicity’ is in our 
conception than it is as usually conceived by biologists. 
We compare our ideas on the subject with those held by only 
one other investigator. Hugo de Vries has dealt with certain 
aspects of periodicity exhibited by plants, quite at length and in 
several of his works. He states the general facts with clearness. 
(De Vries, ’05, p. 721): 
This law of periodicity involves the general principle that every axis, 
as a rule, increases in strength when growing, but sooner or later reaches 
a maximum and may afterwards decrease. This periodic augmentation 
and declination is often boldly manifest, though in other cases it may be 
hidden by the effect of alternate influences. Pinnate leaves generally, 
have their lower blades smaller than their upper ones, the tallest being 
seen sometimes near the apex and sometimes at a distance from it. 
There can be no doubt that the phenomena we are dealing with 
in Salpa and calling periodicity resemble closely those in plants 
thus described. The question, are they ‘exactly the same’ phe- 
nomena, we do not raise. Rather, we ask, in view of the close- 
ness of resemblance ought they or ought they not to be looked at 
from much the same standpoint? The truth is de Vries has 
regarded the phenomena in plants very differently from what we 
have in Salpa, and his standpoint is surely inadequate for the 
facts we are dealing with. ‘‘This dependency on local nutrition,” 
says de Vries, ‘“‘leads to the general law of periodicity, which, 
broadly speaking, governs the occurrence of the fluctuating devia- 
tions of the organs” (p. 721). Again (de Vries, ’01, vol. 1, p. 638) 
under the section, ‘‘ Die Periodicitit semilatenter Eigenschaften,’’ 
we read: 
