Distribution of the Laminariaceoi. 337 



branch of stipe and each with its own transition-place. The posses- 

 sion of this power of splitting longitudinally by the transition-place 

 is characteristic of the members of a tribe of the Laminariaceae 

 which may be called the Lessoniidese, under which may be reckoned 

 two sub tribes, the Lesson ese, represented by the genus Lessonia, 

 Nereocystis, etc. and the Macrocystese which includes only the genus 

 Macrocystis. These subtribes will be discussed more fully below. 

 It is to be mentioned here, however, that the original blade does not 

 persist but its place is taken by the blades split off from it, the 

 place of these by others, and so on. 



There is but one other general type of frond to be noticed and 

 that is well represented by the fronds of any species of Alaria. 

 In these, there is not only a large terminal blade which persists and 

 a simple stipe with the meristematic region situated at the transition- 

 place, but there are also present on the upper portion of the stipe 

 (or the rhachis as it is called) two rows of leaflets or sporophylls 

 (so-called because they alone bear the sori). In Alaria, the sporo- 

 phylls arise as outgrowths on the lower portion of the transition- 

 place, grow larger and larger until they reach a certain definite size 

 when they have come to be situated at some distance below the 

 transition-place which has been carried upward and away from 

 them by the growth of the stipe in length and their places on it 

 have been taken, in turn, by newly formed sporophylls. In this 

 way a simply pinnate frond is produced. 



The essential feature then, of the Alaria-ij\jQ is the formation of 

 a compound frond by means of these outgrowths from the meris- 

 tematic region. The tribe of the Alariidese based upon this type 

 contains three subtribes, the Alarieoe including Alaria and Fterygo- 

 phora, the Egregiese to include JBJgregia, and the Eckloneoe includ- 

 ing EcMonia, Eisenia, etc. 



Above we have glanced at the three general types of adult struct- 

 ure and the modifications of the transition-place associated with 

 each. We are now in a position to consider the details of variation 

 of these types as illustrated by the different genera. 



Lamina RiiDE^. — The members of this tribe, with the exception 

 of Thalassiophyllum Clathrus, P.&R., possess unbranched fronds 

 and all possess unmodified transition-places, unless we except the 

 peculiar scroll-like structures noted below in the case of Agarum 

 and Thalassiophyllum. Under this tribe we may distinguish two 

 subtribes, the Laminariea3 and the Agarese. 



