Dec., 1910.] Self-Dividing Laminae of Certain Kelp ft. 
223 
ment, were used to determine whether the splitting process varied 
in any way with the size of the Lamina. 
The writer is able to confirm in part Will’s account of the 
origin of the basal perforation. Broad shallow furrows appear on 
cither side of the thallus. These depressions may arise as in 
Nereocystis by a relative lessening of anticlinal divisions, but the 
area concerned is so extensive and the slightly constricted portion 
passes so gradually into the normal lamina, that no marked differ- 
ence of tissue structure could be observed. After these shallow 
depressions become well defined, another and wholly different 
process is inaugurated. The inner cortical cells lying under the 
base of each furrow become gelatinized. A single cell disinte- 
grates followed by its immediate neighbors until all the heavy 
walled cortex under the central part of the furrow has disappeared. 
Associated with this process of gelatinization is a marked local 
deepening of the furrows at their central parts (Fig. 13-14.) Will 
states that this originates by a pushing in of the epidermis due to 
increased division of the cells over the gelatinized portion. The 
evidence for this does not appear conclusive as can be seen by com- 
paring the size of the hypodermal cells beneath the furrow with 
those on either side. The cells lying in the base of the furrow 
(Fig. 14) give evidence of relative inactivity, showing a diminution 
in anticlinal and especially periclinal divisions. To the lessening 
of periclinal activity chiefly, can be ascribed the origin of the more 
sharply defined secondary furrow, for the epidermal cells in this 
region fail to build out the thallus. This is somewhat similar to 
the condition in Postelsia. At about the stage figured normal 
growth begins to close in on the gelatinized cavity separating 
schizogeneticallv the remaining cortical cells underlying the 
furrow. The usual gelatin filled pith-web together with the newly 
gelatinized regions of the cortex forms a sort of internal cavity or 
wound which is healed by a process identical with that seen in 
Nereocystis (Fig. 15). Here normal development is bringing the 
respective sides around the edges of the middle layers. The rem- 
nant of one of the gelatinized portions is still present, stretched 
across below the furrow. 
After the original basal perforation is formed in the manner just 
described its advance through the lamina is by a wholly different 
process. Unexpected as this might seem the evidence for it is 
quite conclusive. Fully formed splits 5 mm. in length and upward 
were studied, occurring in laminae of different size and thickness 
and from different waters, British Columbia and Peru, but in no 
case was there any deviation in the process. 
Local and excessive meristematic activity of the cortex is the 
fundamental factor in the advancing cleft. First, however, there 
is a local increase in the normal growth process which results in 
piling up slightly modified cortical cells in the medulla. Next 
