442 W. E. RITTER AND M. E. JOHNSON 
quite the same for individual, and for partial fluctuations’ (p. 
732). And: ‘In the present state of our knowledge the fluctu- 
ation-curves do not contribute in any large measure to an eluci- 
dation of the causes.”’ (p. 734.) 
And so we come to the real issue. Certainly, as de Vries says, 
the differences called partial may be treated en masse, so to speak. 
For example, we might pick to pieces ten wheels of the same di- 
mensions of the Cyclosalpa chain, mix the zooids indiscriminately 
in a dish, then measure them and plot the results. The curve 
would be the same—the normal probability curve—but would 
give us no clue to the way the zooids are disposed as to size in the 
individual wheels. In that case the treatment would not, it is 
true, ‘‘contribute in any large measure to an elucidation of the 
causes.”’ But in our case we have seen that no evidence can be 
found tending to show that the size scheme as it actually does 
occur in the wheels is dependent:on external factors. All the evi- 
dence is to the effect that it is due to the growth process itself 
independently of any correspondingly differentiating external 
conditions. In other words, the periodicity in growth occurs 
- under external conditions, that so far as the evidence goes, are 
not correspondingly periodic. Viewed in this light, can we still 
say the curves teach us ‘‘measureably little about the cause of the 
phenomena under consideration?” It seems to us not. Truly 
they do not furnish us ‘a complete explanation’ of the phenomena. 
They do, however, tell us, seemingly, this much: That the 
cause is in the nature of the growth process itself; that the growth 
goes that way. 
If now it should turn out as suggested that not only the length 
of the zooids falls into a size scheme, but that many of the other 
morphological dimensions, and functional capacities fall into sim- 
ilar schemes, then the instructiveness of the curves would, for us 
at least, be very great touching the causes of the phenomena. 
Whatever view may be held as to the relation of the periodicity 
in plants to that in the Salpa chain, it will we believe be allowed 
that the general question is one of many sides and great possible 
importance to biological theory. We have not pretended to do 
more than call attention to it here. 
