158 ERYTHEA. 



This is shown by the fact that the main flattened portion 

 of the blade no longer increases in length to any consider- 

 able extent, but, by the constantly occurring erosion, becomes 

 shorter and shorter until at last it is worn away, down to the 

 very base, i. e., down to the transition-place itself, leaving, 

 however, the thickened involute margins with the small por- 

 tion of meristematic tissue at the tip of each, projecting like 

 two small arms, one on each side. 



The gradual shortening of the blade at this period in the 

 life history of the plant is very noticeable in the series of 

 specimens obtained by the writer at San Pedro, in which the 

 different stages of the process are very fully represented. 

 In the final stage of the process, where ',the main portion of 

 the blade has practically disappeared, the thickened basal 

 margins project from the summit of the stipe from 3 to 6 

 centimeters. 



A somewhat similar phenomenon, attending the shortening 

 of the blade, takes place in adult plants of the species 

 of Ecklonia. In these the blade proper sometimes 

 becomes very short as compared with the length of the 

 pinnules, thus producing a frond very broad in pro- 

 portion to its length. This is very noticeable in EcMonia 

 hicyclis Kjellm., E. huccinalis (L.) Hornem., a'nd to some 

 extent also in E. radiata (Turn.) J. Ag., but as far as the 

 writer can learn, the process of erosion in all these species 

 stops far short of the transition-place, and a considerable part 

 of the central portion of the blade remains. Although the 

 base of the blade of Ecklonia does not seem to be thickened 

 anywhere upon the margins, yet, in the erosion of the blade, 

 the margins with the pinnules arising from them do not erode 

 as readily as the central portion and are left behind, so that 

 two flaps with pinnules attached are often left extending up 

 from the margins at the top of the blade. These, however, 

 are not at all thickened and do not appear in any way to be 

 homologous with the arms of Eisenia. They simply show 

 that the tissue of the blade which is directly connnected 

 with the sporophylls or pinnules, even when adult, has 



