BoT.— Vol. II.] HUS—POKPHYRA. 1 77 



An interesting instance of great length attained by 

 exposure to the motion of waves in one direction was found 

 in a specimen of P. perforata f. lanceolata, which grew on 

 a rock buried in the sand of the gently sloping shore of the 

 Presidio, San Francisco, California. This specimen attained 

 a length of 325 centimeters, which to the author's knowledge 

 is the greatest length ever attained by any specimen of this 

 species of Porfhyra. This extraordinary longitudinal devel- 

 opment (the average length is but thirty to forty centime- 

 ters) was evidently due to the plants being stretched out at 

 full length every time a wave rolled in or went out. 



P. nereocystis, growing in three to five fathoms of water 

 on the stipes of Nereocystis liitkeana, often attains a great 

 length, specimens of over three meters in length having 

 been collected at Monterey. A specimen of P. variegata 

 collected at Santa Cruz by Dr. Anderson measured seventy- 

 nine centimeters. On the other hand, we have found a 

 fertile specimen of P. perforata but two centimeters long. 

 But the plant which in its adult stage is the smallest of all 

 Pacific Coast species of Porphyra is P. natadum^ which 

 often bears fruit when but one centimeter long. * 



The width of the fronds also varies considerably. While 

 the writer has measured specimens of P. nereocystis which 

 were fully fort3^-nine centimeters in diameter, some mature 

 specimens of P. perforata f . lanceolata collected by Dr. W. 

 A. Setchell at Monterey, California, measured in their 

 widest part but twenty-five hundredths of a centimeter. 



In regard to the part age plays in the determination of the 

 shape of the fronds, it must be said that while the younger 

 plants as a rule possess the elongated type of frond, the 

 older plants generally have a greater width. A microscop- 

 ical examination reveals the fact that the divisions of the 

 cells of the younger fronds are usually parallel to each other 

 and at right angles to the longer axis of the frond. In the 

 older plants, where the development is more isodiametric, 

 we can readily recognize more or less isodiametric groups 

 of cells, which evidently arose from a single cell. Of 

 course, environmental conditions have much to do with this. 



