222 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



The antheridia and sporocarps are intermixed in a mar- 

 ginal zone. Occasionally one or more vegetative cells are 

 found; but this is rarely the case. The antheridia are 

 present in predominating numbers. The reproductive part 

 of the frond has very much the appearance of that of P. 

 mmiata in regards arrangement of sporocarps and anther- 

 idia. Often a cell on one side of the frond will form 

 antheridia, while the corresponding cell on the other side 

 of the frond will form carpospores. 



Sporocarps. — The first division of the sporocarp is per- 

 pendicular to the surface of the frond. This is followed by 

 a division at right angles to it and perpendicular to the sur- 

 face of the frond, or nearly so, thus giving rise to four car- 

 pospores in a single tier, showing in cross-section two 

 carpospores (PI. XXII, fig. 23). The divisions are more 

 or less regular. They may take place simultaneously, thus 

 forming a cruciate division, or they may be consecutive, 

 and the second division in one half of the carpospore is in- 

 dependent of that in the other half. 



Antheridia. — The vegetative division in the antheridium- 

 mother-cell goes one step farther than in the sporocarp- 

 mother-cell, a cruciate division perpendicular to the surface 

 taking place. After this a division parallel to the surface 

 of the frond occurs in each antheridium, followed by a very 

 regular cruciate division perpendicular to the surface of the 

 frond. This last division, however, may precede the paral- 

 lel division. These divisions finally give rise to eight an- 

 therozoids in each antheridium, arranged in two tiers of 

 four each, so that the original antheridium-mother-cell now 

 contains four groups of eight antherozoids each, each group 

 corresponding to a carpospore (PL XXII, fig. 25). 



From the above it will be seen that P. tenuissima possess- 

 es the miniata type of antheridia. It is for this reason that 

 the writer doubts the wisdom of Foslie's action in making 

 P. tenuissima a form of P. amplissima . 



Habitat. — Epiphytic on algae; also on rocks?. 



Distributioti. — As yet only known on the west coast of 

 North America from Alaska (59° 4o'-55° N. lat.). 



