72 A. H. Graves, 
fig. 1, a and 4), which continues the growth of the stem. Of these 
branches, that in the dxil of the upper leaf (Text-fig. 1, a) is invariably 
of stronger growth, exceeding considerably the branch on the other 
side of the floral axis. These axillary branches, after forming a few 
leaves, terminate in flowers again, and the process of branch form- 
ation is repeated. In this way, since the main axis is continued 
by the stronger branch, the system in the region of the flowers is 
sympodial. In most instances, however, the weaker axillary branch 
has a fairly vigorous development, as in Text-fig. 1, in which case 
the branching approximates a false dichotomy, and a characteristic 
fan-like form is thus often produced. 
In Text-fig. 1 the branch a develops two ordinary leaves before 
it terminates ina flower. This brings the upper of the pair of sub-— 
floral leaves at the right side instead of the left, as at I. Such 
an arrangement as this is not as common as is the continual pro- 
duction of the stronger branches on the same side of the stem, 
but in this way also the fan-like form may be attained. 
2. Comparative Study of the Branching of the Potamogetonaceae. 
In Zannichellia, Campbell (1897, pp. 38 ff.) finds that the apex of 
the stem divides into two equal parts, one of which develops into 
the female inflorescence, while the other continues as the main 
axis of the stem. Farther on he says “the inflorescence is the 
result of the dichotomy of the main shoot, whose other member 
continues the growth of the axis.” So that, although a sympodium 
is the ultimate result, it is attained by a dichotomy of the growing 
point, one of the branches becoming a male or female flower. 
Schumann’s (1892) interpretation had been somewhat different from 
this, maintaining that the female inflorescence terminated the main 
axis and that the growth of the shoot was continued by an axillary 
branch arising in the upper of the two subtending leaves. The 
position of these leaves much resembles that of the subfloral leaves 
of Ruppia, so that if Schumann’s idea were correct, the inflorescent 
branch system of Zannichellia would be a sympodium similar in 
origin and development to that of Ruppia. 
Campbell's figures, however, show a vigorous, simultaneous de- 
velopment of the primordia of both flower and main axis, which 
lend to his theory a great deal of weight. In Ruppia the primordium 
of the axillary shoot arises much later than that of the flower, so 
that such a dichotomy as Campbell claims is here impossible. 
(See Pl. IX, figs. 54-56.) 
re eer 
a i i ee ne 
