212 PROCEEDINGS OP THE AMERICAN ACADEMY 



in fairly distinct whorls ; and second, those in which no arrangement 

 into whorls can be traced. 



Laminaria digitata, as limited by the Swedish algologists,* is a 

 good example of the first of these. The primary disk here produces 

 a few hapteres. The second set of hapteres is produced in a whorl, 

 slightly above the region of the primitive disk. As all the hapteres 

 of this whorl start out at about the same time, there is a bulirinfr of 

 the stipe in that region, giving it for a very limited period somewhat 

 the appearance of a rhizogen ; but it does not long continue^ and at 

 no time is there as definite a structure as the rhizogen of the Sacco- 

 rhizce. The hapteres pus^h out very early, and a second whorl soon 

 appears above the first, another above that, and so on. Although 

 there is no real rhizogen present here, yet this whorled arrangement 

 and the consequent bulging appear so very similar as to suggest that 

 the two methods are very closely homologous. 



Of the second class, the common Alaria esculenta, as now limited, is 

 a good example. The primitive disk here produces hapteres, and the 

 next hHpteres above generally come out one by one, and apparently 

 irregularly, although at times they seem to form a more or less 

 regular whorl or two. 



As fiir as the holdfiist is concerned, then, Chorda is the simplest 

 form. Between Chorda and Saccorhiza bidhosa we might expect to 

 find a simple form with hapteres arising from the primitive disk, but 

 we do not. The intermediate form is Saccorhiza dermatodea, with a 

 simple primitive disk and a rliizogen of limited growth. In regard 

 to the holdfast, too, Saccorhiza dermatodea seems directly related to 

 -S. bullosa, on the one hand, and the digitate Lamina) ictp, on the 

 other. 



In structure, Chorda is perhaps the simplest : it has no trumpet 

 hypha?, and few ordinary hypha?. The diaphragms, however, show 

 a complication not present in other genera. Saccorhiza is of more 

 complicated structure than Chorda. It lacks the trumpet hyph;e so 

 characteristic of the other Laminariece, but possesses the peculiar 

 sclerenchyma fibres in their stead. 



Tlie paraphyaes of Saccorhiza are more like those of Chorda than 

 those of the other Laminariecc, being simpler in their structure. 



Saccorhiza dermatodea, then, seems to be of simpler form and struc- 

 ture than any of the rest of the group except Chorda. It is Arctic 

 in distribution, and circumpolar. This simplicity of structure and 



* Cf. Foslic, Die Lam. Norwegens, p. GO. 



