1925] Setchellr-Gwdner: Melanophycecu 591 



indications to their seemingly logical outcome has led us to arrange the 

 Brown Algae as we have, trusting to be justified, at least in large 

 measure, when our knowledge of development within the group shall 

 have been made more exact. The order of the Laminar iales, however, 

 is clearly delimited by the intercalary region of growth in the complex 

 plants belonging to it associated with the intermingling of the uni- 

 locular zoosporangia with unicellular paraphyses in extensive elevated 

 aori. The question as to the division of the order into families is not 

 so clear as that of its cleavage from other orders. Two families have 

 been recognized and there is great temptation to increase the number. 

 There certainly exists a certain tendency to group genera into some 

 sort of larger divisions, but the difficulty lies in finding sharp lines of 

 cleavage. The best distinctions lie according to the differentiations 

 of the frond arising at the transition place between the blade and the 

 frond and the relation to this and the fertile areas. The alternatives 

 Beem to be these: either to retain all the genera under one large and 

 varied family (possibly excepting the Chordaceae) divided into num- 

 erous tribes, or to divide them between numerous families of unequal 

 value and of often indistinct cleavage. We have separated the Lami- 

 nariaceae into five families, one of which Haligeniaceae (including 

 Haligenia and Sasccorhiza) is not represented in our territory. 



Key to the Families 



1. Stipe absent or not differentiated, paraphyses without hyaline appendages 



19. Chordaceae (p. 591) 



1. Stipe distinct, at least when young, paraphyses with hyaline appendages 2 



2. Transition place neither giving rise to splitting nor to outgrowths 



20. Laminariaceae (p. 593) 



2. Transition place not as above 3 



3. Splitting arising at transition place or within its influence 



21. Lessoniaceae (p. 621) 



3. Outgrowths arising at transition place or within its influence 



22. Alariaceae (p. 633) 



family 19. CHOEDACEAE dumort. 



Fronds cylindrical, hollow, interrupted by diaphragms, with a 

 discoid holdfast, growth in length basal (situated just above the hold- 

 fast), innermost cells elongated, supporting hyphal filaments united 

 to form the diaphragms ; outermost layer a single row of slightly elon- 

 gated cells with colorless hairs and with or without exserted colored 

 filaments ; sori extended, paraphyses destitute of colorless appendages ; 

 gametophyte microscopic as in the order. 



