III. OBSERVATIONS ON PELVETIA. 



F. L. Holtz. 



Pelvetia fastigiata (J. Ag.) DeToni, is a marine alga found 

 distributed along the western coast of the United States and 

 British Columbia. It grows in beds, attached to the rocks, be- 

 tween high and mid tide, and is, therefore, daily exposed to the 

 air for several hours (PL VIII.). The material studied for 

 this paper was collected by Miss Josephine E. Tilden on Van- 

 couver Island, in June, August, and December, 1901, and was 

 preserved in formalin. 



There was originally some doubt in the minds of systematists 

 whether this plant was a Pelvetia. It has been called Fucus 

 fastigiatum (J. Agardh, Symb., I., 3) and Fucodiunv fasti- 

 giatum (J. Agardh, Sp., I., 203). The difficulty of placing 

 it arose from the uncertainty as to the number of eggs it forms 

 in the oogone, and this point was left undecided by DeToni. 

 Dr. W. A. Setchell seems to have been the first to demonstrate 

 the true generic position. * 



External appearance. — Pelvetia is one of the smaller wracks. 

 It is 10-20 cm. in height, and springs from a disc-shaped hold- 

 fast with dichotomous branches repeated till it presents a fasci- 

 cled appearance. In well-developed plants the stipe branches 

 immediately above the holdfast, and the branches subdivide 

 again but a short distance farther on, so that at first sight there 

 seems to be several fronds arising from the same holdfast. The 

 regular dichotomy near the base may be further confused by 

 adventitious shoots springing from near the base of the main 

 stipe. In the material at hand but one main stipe was observed 

 arising from a holdfast. The front may undergo dichotomy a 

 dozen times before the terminal laminae are reached. The inter- 

 nodes are longer toward the top. The coordinate branches 

 keep about equal growth, though a few may remain smaller and 

 hence appear like lateral branches (PI. VII). 



* Setchell, W. A. Phvc Bor. Am., No. 176. 



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