WEBER-VAN BOSSE—MARINE ALG A 291 
apical cell, and a much denser ramification. The absence of trichoblasts is no reason 
to separate O. Prainit from the genus Oligocladus, for in the genus Polysiphonia we 
find species with and without these organs. 
The main axis of the plant was attached by means of its long rhizoids to the 
branches of Dasyopsis, and, as may be seen in fig. 31, the youngest part raises itself 
from its support, grows vertically upwards, though its apex shows a slight curve. The 
apical cell is rather long and cuts off the segments at its base by a transverse wall. 
These segments remain undivided for a long time—I have counted eight of them under 
the apical cell before the pericentral cells are begun to be cut off. 
The dorsally placed branches arise irregularly with a distance of 3, 4, 6, 7, 8, 9, and 
even more segments between them; they bear branches of the second order on the side 
turned towards the main axis. In some cases I observed near the apex of the main axis 
long ramified branches alternating with short-simple ones, but in later stages I could 
detect no further difference. Perhaps the long ones bear the tetrasporangia and the 
short ones remain sterile, but this is a mere suggestion. The first segment of the 
branches issuing from the main axis has only short pericentral cells; the second 
segment has pericentral cells of the normal size; all the branches of the first and 
second orders arise from the central tube. ‘The size of the branches and of the main 
axis differs considerably according to the place where the measurement is taken. The 
main axis has a breadth of 120-2004; the branches 40-80 in the lower parts, but at 
the top only 12-20; the segments are 13 times as long as the diameter, and at the 
top as long as broad. 
At the top of the main axis all the branches are arranged on the dorsal side of the 
filament, but at some distance from the apex their position is sometimes altered ; this 
is the result of a slight twisting of the cells of the main axis. 
2. OLIGOCLADUS PUSILLUS, 0. sp. 
Thallo filiformi, repente ; ramis erectis, endogenis, simplicibus, normaliter dorsaliter 
exeuntibus. Filisconstantibus ex uno ordine cellularum centrali et quatuor ordinibus 
cellularum pericentralibus. Trichoblastis numerosis, filorum apices cingentibus. 
Filis latis 40-100 ». Organis fructificationis ignotis. Rhizoidis unicellularibus. 
Coetivy, reef, on Dasyopsis aperta; im alcohol. 
Oligocladus pusillus, on account of the numerous trichoblasts that surround the 
slightly curved top, stands nearer to O. Boldinghii than O. Pram. It is a smaller 
plant, though its filaments are broader. Its creeping filaments give off side-branches 
on the dorsal side at a distance of 5, 7,12, 20 segments and even more. ‘These 
ascending side-branches remain simple; when, however, they develop into creeping 
filaments, as occasionally happens, they likewise give off branches on their dorsal 
side. The creeping branches have a diameter of 100», the side-branches a little less, 
and at the top of both the diameter sinks to 40. The segments have a height of 
80-100 p, but this sinks at the top to 20 » and even less. 
Organs of fructification have not been observed. 
