Download PDF

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
3. Outgrowths arising at transition place or within its influence
family 19. CHOEDACEAE dumort.
21. Lessoniaceae (p. 621)
22. Alariaceae (p. 633)
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.
;