102 AXXAL> OF 5COTTI.M1 NATURAL HISTORY 



branched, with distinct main axis, with branches of at least four 

 orders. The branches are of two kinds : long branches with many 

 cells, and short ones with from one to ten cells. The former are tew 

 in number, and issue partly alone, partly in pairs opposite to each 

 other. The short branches are numerous ; by these the present 

 species is easily recognised from P. HforaHf. In long parts of the 

 frond such a branch issues from every cell. They are always isolated, 

 and issue at a right or nearly right angle. The long branches are 

 somewhat attenuated towards the tip, and generally end in some long 

 hair-cells. The short branches are cylindrical or slightly claviform, 

 with an apical cell rich in endochrome, which cell is finally trans- 

 formed into a zoosporangium. 



" The cells of the frond are usually short, cylindrical, or slightly 

 tun-shaped, equally or even twice as long as thick. The cells which 

 give rise to a long branch are commonly short. If a short branch 

 issues from a cell which is longer than thick, as is often the case, the 

 branch is almost always placed at the middle of the longer wall. 

 The thickness of the principal axis is about Sop.. With the exception 

 of the hair-cells, all the cells are rich in granular, equally distrib: 

 endochrome. The development of the zoosporangia, and their 

 arrangement thereupon, are subject to very great variations, 

 zoosporangia are sometimes arranged as in /'. literalis. In a modi- 

 fication of this type all the cells, not only the ultimate ones, are 

 transformed into zoosporan^ - >metimes only the apical cell 



becomes a zoosporangium, and the branch is composed of one or 

 more cells. It also often happens that a greater or less number of 

 cells are divided by longitudinal or oblique walls, and that it is the 

 secondary cells produced by this division that are developed into 

 zoosporangia. In this case the division of the cells and the develop- 

 ment of the zoosporangia sometimes take place in such a manner 

 that the zoosporangia become arranged in whc : 



The above description applies exactly to a seaweed 

 which I detected in a parcel of specimens collected in 

 Cromarty Firth, and forwarded to me last year by Mrs. M. 

 Farquharson of Meigle. It formed dark brown, den.-c. 

 entangled rope-like tufts, and by reason of the short hori- 

 zontally patent ramuli, it was distinguishable at once from 

 the ordinary forms of Pylaiella litoralis, Kjellm., which were 

 present in the same parcel. The latter could easily be 

 spread out naturally in sea water, but with P. --aria it was 

 impossible to do so, owing to the felting of the ramuli. The 

 plants were abundantly fruited, having unilocular zoospor- 

 angia : sometimes in a short moniliform series of four or five, 

 formed at the expense of one of the short lateral ramuli, and 



