THE AMERICAN NATURALIST [Vol. XLIII 



Some speculations as to the nature and significance of 

 this cone may be of interest. Of all the kelps Renfrewia 

 and Cymathere are the only ones in which the mature 

 holdfasts are restricted to the primitive disc region. In 

 the development of the latter genus, as traced by the 

 writer ('07), there is no indication of such an organ as 

 can be seen by an inspection of the figures then published. 

 Phyllaria and Saccorhiza differ in their holdfast char- 

 acters from all the other genera. Instead of putting out 

 hapteres directly from their stipes they develop bulbous 

 "rhizogens" which form ring-like collars around the 

 stipe. From these the hapteres are formed by unequal 

 growth along their margins. Though the rhizogen in both 

 genera is separated from the primitive holdfast by a dis- 

 tinct interval on the stipe, it is essentially similar to the 

 basal cone of Renfrewia which we may consider as an 

 incipient rhizogen. This would indicate some leaning of 

 Renfrewia toward the Phylariatse; but its paraphyses 

 are of the typical clavate form not at all similar to the 

 linear ones of that group. Whether this basal cone is a 

 nascent organ representing the beginning of the holdfast 

 or is a vestige of a Saccorhiza-like rhizogen is a puz- 

 zling problem. At some stage in their history the rhizo- 

 gens of Saccorhiza and Phyllaria probably passed 

 through this condition and remained for a longer or 

 shorter period without further development. On the 

 other hand, the obscuring of the cone in Renfrewia when 

 adult might suggest a vestigial organ. Perhaps the best 

 hypothesis is that Renfrewia was cut out from the main 

 advancing phylum of the kelps, isolated and fixed, at the 

 stage where the tendency to form a secondary holdfast 

 was just beginning to manifest itself. 



The tissues of the many-layered lamina of Renfrewia 

 are apparently acquired after the fashion of other kelps, 

 but in Renfrewia the many-layered lamina begins its de- 

 velopment in smaller plants than in the Phylariatae in- 

 cluding Cymathere. Even in the smallest specimen 

 (Fig. 1) there is only a small portion of the one-layered 

 blade remaining around the edge of the lamina. In the 



