56 Puget Sound Marine Sta. Pub. Vol. 1, No. 8 



the sporangia are the longer, sterile filaments or paraphyses. These 

 fit into a mucilaginous pellicle, which seems to serve as a protection to 

 the young sporangia. In the mature condition this pellicle seemed to 

 be sloughing off to permit the free discharge of spores. 



The most interesting feature of the holdfasts is their tendency to 

 send out hapteres only from the edges of the flattened stipe. Those on 

 the flattened sides tend to remain unbranched and small {Fig. 6). Not 

 all showed this so strongly as the specimen figured, but in all specimens 

 the tendency was evident. They branch freely dichotomously, and show 

 the structure of hapteres usual in Laminariaceae. 



SUMMARY AND CONCLUSIONS 



1. The chambers do not arise abruptly, but develop gradually from 

 rifts formed in the pith tissues. 



2. These rifts evidently occur as a result of combined linear and 

 lateral strain. 



3. This strain is apparently produced by the continuation of trans- 

 verse and radial division of the cortical cells, after the cells of the 

 medulla have ceased dividing. 



4. A continuation of this severe strain breaks down the sieve-tubes. 



5. Hyphal chains of cells torn asunder by chamber formation also 

 soon deteriorate, losing their cellular structure. The torn chains of sieve- 

 tubes and hyphal cells break down, forming a mucilaginous substance. 



6. The continued growth of the cortical cells, after the sieve- 

 tubes break down, causes elongation of the walls of the chambers. 



7. The septa are made up chiefly of hyphal chains not broken by 

 strain. 



8. The variation in the length of the chambers is evidently due 

 to the breaking of the sieve-tubes at the regions of greatest strain. These 

 legions would naturally occur at unequal distances apart. 



9. Specialized sieve-tube areas are developed at the extremities of 

 the pith area. They appear to prevent undue elongation and strain 

 from tearing down the midrib. They probably also serve as conducting 

 vessels after the pith is broken down. 



10. Normally the hapteres arise chiefly or wholly at what corre- 

 sponds to the edge of the lower portion of the flattish stipe. Those 

 arising from the flattish sides tend to remain small and unbranched. 



11. The sporangia and paraphyses develop as they do in Nereocystis. 



