Dec, 1910.] Self-Dividing Laminae of Certain Kelps. 223 



ment, were used to determine whether the spHtting process varied 

 in an\' way with the size of the Lamina. 



The writer is able to confinn in part Will's account of the 

 origin of the basal perforation. Broad shallow furrows appear on 

 either side of the thallus. These depressions may arise as in 

 Ncrcocystis 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 furrow's at their central parts (Fig. 13-14.) Will 

 states that this originates by a pushing in of the epidemiis 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 

 schizogcnetically 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 

 w^ound which is healed by a process identical with that seen in 

 Nereocystis (Fig. 1.'5). 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 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 



