OF ARTS AND SCIENCES. 



lOl 



oar-shaped base characteristic of these old specimens, and expanded 

 gradually until it reached the truncated apex. It was 58.4 cm. long, 

 and 12.7 cm. wide at the top. 



A curious thing to be observed in tlie specimens cast ashore is that 

 the great majority of them lack the holdfast, although the attachment 

 by this organ does not seem to be a very firm one ; for if one catches 

 hold of a growing plant, even by the tip of the blade, and gives it a 

 strong and sudden pull, it almost always comes away from the sub- 

 stratum uninjured, olfering in this respect a strong contrast to the 

 ordinary species of the Laminar iece. But the majority of the old 

 specimens cast ashore in the spring look as if they had been twisted 

 off at the lower end of the stipe, and occasionally a bunch of fionds 

 will be found cast up, all twisted togdther in a most complicated 

 manner. 



This species appears to be an aniuial. De la Pylaie * and Ares- 

 choug t were also of this opinion, and all the data that are at hand 

 seem to support it. On the coast of Massachusetts I have never seen 

 an adult plant after May (when old, decaying, fructified specimens 

 were cast ashore) until September. The plants growing in the pools 

 become very battered and torn, and covered with parasites in De- 

 cember and January ; and the adult plants found in the springtime are 

 always very old and about to decay. There is, besides, no indication 

 in the structure that the plant is either biennial or perennial. 



Summary. — From what has been said above, it will appear that 

 each of the four periods into which the life-history has been divided 

 for convenience has its characteristic features. 



The lack of suitable material, and the small size of the germinating 

 plants, prevent any satisfactory discussion here of the changes taking 

 place in the first period and the early portion of the second. Toward 

 the end of the second period, however, the young plant is provided 

 with a distinct disk for attachment, a short cylindrical stipe, and a 

 blade which for the most part is more than one layer of cells thick. 



The third period has for its characteristic feature the development 

 of the permanent holdfast. A small swelling, the rhizogen, appears 

 a short distance above the primitive disk, increases in size, and pro- 

 duces two whorls of short fibres, the hapteres, one above the other. 

 The hapteres attach themselves to the substratum by their tips. 



The fourth period extends to the death of the plant. In all the 

 preceding stages the base of the frond has been narrowly cuneate, and 



* Fl. Terre Neuve, p. 49. 



t Obs. Phyc, Part. III. p. 12. 



