12 



VARIATION AND DIFFERENTIATION IN CERATOPHYLLUM. 



Fig. 2. — Diagram of Ceratophyllum 

 plantjShowing plan of making record. 

 A, main stem; A',A"y secondary main 

 stem; B, B, primary branches; B', B', 

 secondary branches; B", tertiary 

 branch; B'", quaternary branch, The 

 numbers indicate the manner in 

 which position is recorded. 



or not dichotomy of the main stem has 

 occurred. Consequently each case of this 

 kind was decided by a careful examina- 

 tion of the parts, and if it was found that 

 each of the two axes possessed the charac- 

 teristics of main stems they were recorded 

 as ' ' secondary main stems. ' ' 



The whorls on each of these divisions 

 of the plant (main stem, secondary main 

 stem, primary branch, secondary branch, 

 etc.) were numbered consecutively, be- 

 ginning with the most proximal as 1. In 

 this way the position of every whorl on 

 the plant was recorded. These position 

 records also gave the size, as measured 

 by number of whorls borne, for each di- 

 vision of a plant. Furthermore, in record- 

 ing a whorl from the axil of which one 

 or more branches arose, a note was made 

 of the origin of branches at that point. 



The whole system of records will be 

 made plainer by reference to a diagram of 

 an imaginary Ceratophyllum plant. Such 

 a diagram is given in fig. 2, in which the 

 whorls are represented by short cross 

 lines. It will, of course, be understood 

 that in an actual plant the branching 

 would usually be much richer than is in- 

 dicated by the diagram. The diagram 

 shows, however, that our records were 

 such that we could reconstruct from 

 them the entire plant as it existed. Thus 

 the record on our data slips of a whorl 

 like that marked with an x in the diagram 

 would, when translated, signify that this 

 whorl was the fourth whorl on a secon- 

 dary branch from which no tertiaries 

 arise and that this particular secondary 

 branch sprung from the axil of the second 

 whorl of a primary branch, which in turn 

 arose at the ninth whorl of a secondary 

 main stem beginning just beyond the 19th 

 whorl of the original main stem. Since 

 our records are of this kind for every 



