VARIATION IN DIFFERENT PORTIONS OF PLANT. 



47 



plus. In fact, Series III forms the only exception to this rule. This 

 exception arises from the fact shown in table 28, p. 52 that the tertiary 

 branches tend to be more variable in length than is the case in the other 

 series. It will be shown in later sections of the paper that the positional 

 differentiation of whorls within an axial division of the plant is such that 

 the variation exhibited by groups of whorls may be greatly influenced by 

 the length of the branches on which they are borne. 



Table 23. — Constants for variation in whorls on tertiary branches. Totals for series. 



(c) The tertiary-branch whorls thus appear to be differentiated as a 

 class from those borne on other portions of the plant. 



Turning to the whorls on quaternary branches, we have, unfortu- 

 nately, only a single series which gives any data at all. In our experience 

 the extreme condition of lateral growth implied in quaternary and higher 

 order branches is very rare. It seems possible that this may be due 

 merely to the restriction imposed by the shortness of the growing season. 

 The finding of quaternary branches in the plants of Series V lends 

 support to this view, for the reason that, as has been pointed out above 

 (p. 15) the large plants in this series had wintered over and were grow- 

 ing like perennials. An examination of Ceratophyllum from more 

 southern latitudes would be interesting in this connection. 



