192 PROCEEDINGS OF THE AMERICAN ACADEMY 



it has been difficult to determine either where the stipe ended or where 

 the blade began ; but at the beginning of this period occurs the pro- 

 cess compared above to tlie process of the renewing of the blade in 

 other Laminarieae, after which the boundary between stipe and blade 

 is well marked, and the blade itself becomes thicker and firmer, and 

 ceases to possess cryptostomata. When this set of changes has fairly 

 ended, the zoosporangia are produced, and the plant, having served its 

 purposes, dies, and gives place to a new generation. 



Histology. 



Having thus considered with some detail the various morphological 

 changes which Saccorhiza dermntodea undergoes in the course of its 

 life-history, we are in a position to turn to the histological changes 

 which take place during the same period. 



Literature. — The histology of this species has been seldom referred 

 to. De la Pylaie's account* does not express to us any very definite 

 idea. Areschoug t has described the structure of the cryptostomata 

 and of the organs of fructification. KjellmannJ has spoken of the 

 structure of the stipe, and especially mentioned the " very long tubular 

 cells, with very thick walls," found in this organ in this species, and 

 lacking in the Pliyllaria lorea found by him at Spitzbergen and Nova 

 Zembla. Barber, as mentioned above, has described the histological 

 changes occurring in connection with the development of the bulb in 

 Saccorhiza bulbosa, De la PyL, and has thus furnished a valuable 

 means for comparing these two species. 



The account of the histology will be arranged according to the 

 periods of development sketched out above. 



First Period. — The first period begins with the zoospore and its 

 germination to form a filament of a single row of cells, and extends to 

 the formation of a membrane of a single layer of cells in thickness. 

 No plants of Saccorhiza dermatodea belonging to this period have 

 been seen, but evidences of the existence of these early stages are 

 present in the youngest plants known. 



As far as I know, Thuret § is the only one who has described or 

 figured either the zoospores or germinating plants of any species of 

 the Laminarieee. He figures the entire development of Saccorhiza 

 bulbosa II for this period, as well as the early stages of Laminaria 



* Fl. Terre Nenve, pp. 50 to 52. t Obs. Pliyc, Part. III. p. 12. 



X Arct. Alg., pp. 224 and 225. 



§ Ann. Sci. Nat., Ser. 3, Tom. XIV. PI. 29 and 30, 1850. 



II Loc. cit., PI. 30, Figs. 5 to 10. 



