EISENIA A15B0EEA. 159 



greater vitality than the undifferentiated central portion. 

 It is very much the same in Eisenia, only in this case, the 

 tissue is exclusively basal and even more vigorous ; the 

 differentiation also, is carried further, and the two arms are 

 the result. 



After the erosion of the blade has been completed the 

 plant has all the essential characters of the adult. The stipe 

 increases in length through the activity of the meristematic 

 layer at the transition-place, and in thickness by secondary 

 processes within itself. The arms in turn increase in length 

 by the activity of the meristematic layer at the tip of each. 

 They increase in thickness, through secondary growth, until 

 they rival the stipe itself in this respect and certainly come 

 to look more like derivatives of the stipe than like deriva- 

 tives of the blade. The sporophylls (or pinnules as the 

 earlier sterile ones were called) arise continuously at the 

 lower edge of the ligules, and wearing away, the older ones 

 are lost, together Avith the upper edges of the same struc- 

 tures, as has been described above. 



Abnormal Branches. 



One very interesting case of branching was observed by 

 tbe writer in a specimen cast ashore upon the beach at San 

 Pedro. It was a fairly large plant, somewhat battered, yet 

 showing very plainly that one of the arms had been lost 

 The other arm however after reaching a considerable length 

 had divided again and produced two arms in turn, equal in 

 every respect, and each bearing a ligule with its bunch of 

 sporophylls at the tip. These two secondary arms were in 

 every way like the two produced normally in the species. 



General Considerations. 



The general course of the development in Eisenia follows 

 that already known in several other Laminariacese in which 

 the ontogeny repeats, or appears to repeat, to a certain 

 extent the phylogeny of the form. The earliest stages 

 described consist of a simple stipe, holdfast, and unmodified 



