MacMillax: Observations on Nereocystis 



277 



gradually enlarges distally into a portion which afterwards under- 

 croes a lateral flattening into lamina. The pneumatocyst originates 

 as a swelling in the stipe just below the lamina and is the last of 

 the three distal members to come into existence as such. At first 

 the lamina is single and uncleft, of a rather narrow, lanceolate 

 shape and becoming narrowly ovate with acute tip as it grows older. 

 The first longitudinal slit which separates the lamina into two 

 halves right and left appears near the base of the lamina (accord- 

 ing to my series of young forms) when the length of the whole 

 plant has reached about 1 3 cm. This cleft is the only one which 

 reaches clear to the surface of the pneumatocyst though the second 

 cleft comes very close and divides the two laminae into four. Oli- 

 ver's statement, no doubt based upon an incorrect figure of Postels 

 and Ruprecht, that as a rule five petioles are borne upon the pneu- 

 matocyst is quite unconfirmed by any of the plants which I have 

 examined. On the contrary as pointed out by Areschoug there 

 are but two main distinct laminae each of which is cleft almost to 

 the base by the secondary longitudinal furrows and tertiary and 

 successive furrows cleave these laminae almost to the base, so that 

 a hasty examination suggests the presence of two tufts of leaves. 



In each tuft there may be twenty-five or more lobes or leaves. 

 The resemblance of the leaf arrangement to that in Areschoug's 

 Pdagophyciis giganteiis, a plant of the Californian coast and by some 

 American students still maintained to be congeneric with Nerco- 

 cystis Liitkeana, is certainly very demonstrable. 



The origin of the clefts and of the pneumatocyst is better dis- 

 cussed in the histological portion of my paper but the primitive 

 differentiation of lamina and stipe, since it arises simply by the 

 lateral flattening of a primitive piriform distal bulb, may be noted 



I 



here. At first the lamina is shorter than the stipe but after the 

 plant has become about a tenth of a millimeter in length the lamina 

 begins to elongate relatively faster for a time, but when the plant 

 has reached a length of twelve or thirteen centimeters the elonga- 



tion of the stipe beconies relatively more rapid and this ratio con- 

 tinues so that in a plant eighty feet long the stipe measures forty 

 feet, from hapteres to pneumatocyst, and another forty to the tips 

 of the slender ribbon-shaped lobes of the two great leaves. But 



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