1915 Kibbe; on Alaria 53 



linear growth causes the chamber to become successively ovate and pyri- 

 form. Continued growth from only one end of the rift causes it to 

 remain a solitary chamber. The chamber is cleared of hyphae by their 

 dissolution, as in ^. fistulosa. 



Another item of interest regarding the structure of A. fistulosa 

 should be noted. The cortical cells are very noticeably pitted; in many 

 cases the protoplasmic connections show plainly within the pits. As 

 noted by Sykes in Macrocystis (4), the pits have an appearance which 

 suggests puckering of the surrounding membranes. They are found 

 chiefly around the outer margin of the cell. The side walls of these 

 cells, as viewed in longitudinal section, are simliarly pitted, the num- 

 ber of pits averaging slightly lower. In A. valida these pits were 

 almost wholly wanting in the sections examined ; only a few scattered 

 ones were seen. 



The sporophylls of A. fistulosa are found along the sides of the rachis, 

 from 60 to 200 being produced by each plant. They arise from ridges 

 of tissue thrown out at the sides of the rachis {Fig. 6). The pith 

 web enters this ridge {Fig 11) and presents a somewhat rifted ap- 

 pearance. The ridge becomes more and more irregular in outline, at 

 last breaking up into small leaf-like bodies {Fig 8), into which the 

 pith web freely enters. The pith web is sent out from the pith area of 

 the medullary region of the rachis. 



The young sporophylls were sectioned, and the origin of the 

 sporangia was traced from the formation of the paraphyses {Fig. 7) 

 to the mature stage of the sporangium {Fig. 9). Their development 

 was found to be similar to that of Nereocystis, as determined by Mac- 

 Millan (2). The epidermal cells divide transversely, the outer cells 

 being modified to form paraphyses. At the base of each paraphysis a 

 bud is sent off, which forms a sporangium. Not all sporangia arise at 

 one time, hence their varying sizes enable them to fit together to form 

 a fairly regular layer of sporangia. In mature sporophylls, raised 

 papillate bodies are noted on the surface. These seem to be caused 

 largely by an over-crowding of the surface by mature sporangia, thus 

 necessitating increased area. At the base of this raised portion {Fig. 

 24) the pith web thickens, evidently to strengthen the tissues to resist 

 strain. In some cases a rift is made by this strain, but more commonly 

 the cells enlarge to fill the increased space. 



The sporangia are flask-shaped, and contain varying numbers of 

 spores. The number of spores produced by one sporophyll is extremely 

 large. The sporophylls on an entire plant produce so many spores that 

 this plant presents an extreme case of over-production, necessitated by 

 the great loss of spores after discharge from the sporangia. Among 



