276 MacMillan : Observations on Nereocvstis 



The primitive disc finally stands near the center of the great 

 fixation-organ made up of the haptcrcs progressively developed 

 from above. If growing upon a flat surface, the ends of the hap- 

 teres originating from higher whorls on the stipe stand concen- 

 trically outside of those belonging to hapteres of lower whorls and 

 the whole apparatus is to be diagrammed as a series of superposed 

 cones very much flattened and split. 



In old material of Nereocystis 3. great many confluent callosities 

 may occur along the stipe. These originate from emergences 



precisely similar to those which produce haptcric branches and 

 probably the callosities may be regarded as homologous with un- 

 attached hapteres. I have not observed dichotomy in any of the 

 callosities nor need I discuss at length their probable function. It 

 suffices to indicate their great similarity of origin to the secondary 

 hapteres, suggesting that the whole stipe is capable of forming 

 holdfast organs from the base to the pneumatocyst. The callosi- 

 ties are sometimes as large as one's finger and spirally disposed 

 around the slender stipe reminding one a very little of a loose 

 growth of Cuscuta on the stem of a flowering plant. This posi- 

 tion I regard as indicating torsions of growth in the stipe and it 

 has been clearly observed that while the elongated callosities are 

 in some cases confluences, in others thcv orimnate from sing^le on- 

 ginal hemispherical protuberances. On the stems of young plants 

 a foot or two in length the callosities are extremely rare, but they 

 progressively develop and increase in number and size until old 

 stems are abundantly provided with them along much of their ex- 

 tent. They are particularly in evidence when two or more plants 

 growing close together have twined about each other as they often 

 do. On the stipes of such the callosities are developed as a con- 

 tinuous cushion where the stems are in contact. Although really 

 organs of the stipe, I have mentioned these callosities at this point 

 because of their evident homology w^ith the hapteres. 



The distal end of the Nereocvstis plant finally differentiates it- 

 self into three areas, stipe, pneumatocyst and lamina. When very 

 young no distinction between these areas is visible, but in the smallest 

 plants I have seen — and they may possibly be Costaria^ Lauiinaria 

 or ^^Azr/^ sporelings rather than those of Nereocystis — the stipe is 

 marked off by a sharp constriction from the primitive disc and 



