190 Phillips . — The Development of the Cystocarp 
vein, as shown in Harvey’s figure, but this vein arises only 
after the establishment of the cystocarp. 
When the manner of growth of the thallus comes to be 
considered, D. simiosa presents a marked contrast to the 
species already dealt with. In these there is present at the 
geometrical apex a single conspicuous cell, which, by its 
repeated transverse divisions, gives rise to the axial row, the 
cells of which never divide transversely again, and from which 
later cells are cut off longitudinally by divisions which do not 
pass through the organic axis. The pericentral cells thus 
cut off repeat, in a modified form, the behaviour of the apical 
cell, and thus the thallus arises. Were it possible to isolate 
the pericentral cells with their respective products, the whole 
thallus would resolve itself into a system of branched filaments 
like a Callitkamnion . The growth is apical, in the sense 
that multiplication of cells takes place at innumerable apices, 
of which the most important coincides with the geometrical 
apex, the others lying at the margin and surface, or imbedded 
in the substance of the thallus. This method of growth 
Schmitz at first regarded as characteristic of all the Red 
Seaweeds, exclusive of the Bangiaceae. Naegeli and Schwen- 
dener (’67), in their work on the Microscope, had already 
selected D. simtosa and Nitophyllum laceratum as typical 
cases of growth by intercalation, which they illustrated by 
figures. Returning to this subject in his later writings, 
Schmitz (’92) conceded the whole tribe Nitophylleae (including 
D. sinuosa ) as affording evidence in the structure of the 
thallus, sooner or later, of intercalary growth. He demurs, 
however, to the figures of Naegeli and Schwendener, which, 
he said, left much to be desired. He seemed still to deny 
that the growth in thickness of the thallus of Nitophyllum 
is ever due to intercalation, and in particular he refused to 
acquiesce in Johnson’s (’92) suggestion that the callosities of 
Nitophyllum versicolor afforded an instance of growth by 
intercalation. With regard to the growth in thickness of 
the thallus in the neighbourhood of the cystocarps, in both 
Nitophyllum and D. sinuosa , my own observations convince 
