138 



has a hypothallus with cells of the same size, whereas No. 1546 11 

 seen from below, has a hypothallus with cells of different size 

 constituting a principal axis of larger cells from which spring 

 files of smaller cells, that form together groups, like elongated 

 little fans. 



The frond of No. 1546 11 is rather thick, it must be an old 

 plant and I think that by succeeding growth, changes in the basal 

 layer of the frond have taken place. Only too often, when stu- 

 dying Peyssonnelia , one sees that the basal layer undergoes 

 changes, and these can ultimately tend to the solution and even 

 disappearance of part of the hypothallus. In P. Boergesenii the 









Fig.' 143. Peyssonnelia Boergesenii nov. spec. View of two hypothalli, loo- 

 sened from the substratum, a. (No. 1442) young hypothallus. "principal axis 

 not yet differentiated, b. old hypothallus with distinct principal axis. (No. 



1546 ii). (210:1). 



hypothallus is not soluted ; the cells of the principal axis increase 

 simply in size. 



The apical cells is long and as high as or less high than the 

 cells of the basal layer (Fig. 144) l ) and in this respect P. Boerge- 

 senii differs from P. Nordstedlii that has a high, short apical cell, 

 like Fig. 140. 



The perithallus (Fig. 145) consists of a Jower part of almost 

 square cells, high d=40^, on which follows an upper part with 



The section after which this figure was made, did not quite satisfy 

 me; I fear that it is a section throng a margin no longer in a grow- 

 ing state, but I could get no better for the margin of the alga was 

 very much broken off. This section shows, however, that the apical 

 cell is not a high, short one. 



