550 KELLICOTT : PERIODICITY IN ROOT OF ALLIUM 
feature ; it is quite likely that the rate of elongation increases uni- 
formly from I1 p. m. until 7 a. m. 
These time relations, however, do not lead to the understanding 
of any causal relation more definite than that expressed by Ward,* 
that the energy of the cell is not sufficient to enable it to continue 
its growth and at the same time form new cellular elements ; there- 
fore when the cell is dividing and the new cell-wall forming, etc., 
the energy of the cell is diverted from its other growth-processes 
and elongation is arrested. Rhythmic activity resulting from the 
uniform action of stimuli or forces is quite universal and it may be 
that here in the root where external conditions are practically uni- 
form, we are dealing with a rhythm which is not related directly 
to the external environment, but which results from the activity of 
the root itself, z. ¢., is internal in its origin. There can be no doubt 
that the rhythm in the stem is to a greater or less extent an in- 
duced one, and it is difficult to believe that the pronounced rhythm 
of the stem is without influence upon the root; yet in the roots 
of these bulbs without growing aerial organs, definite rhythms are 
established. We should know whether this rhythm of the root 
is maintained unchanged after the development of the leaves with 
their marked daily rhythm. With our present limited information 
we are hardly justified in making assumptions as to what are the 
causal relations between cell-division and elongation, both to each 
other and to the other vital activities of the plant. 
* Ward, H. M., Joc. cit. 
CoLUMBIA UNIVERSITY, 
J 4. 
