76 SEAWEEDS 
the frond, these sori are more or less localised, though 
usually of variable and irregular outline. The 
thallus is in nearly all cases of considerable size, in 
some of gigantic proportions exceeding in length 
all other plants (Macrocystis) and attaining a girth 
(Lessoni) comparable with that of trees. The brown 
tangles of our seas are typical representatives of the 
order. In all cases except Chord there is a 
differentiation of stalk and blade, and the growing- 
point, which is an intercalary group of meristematic 
cells, is situated at their junction. In point of 
differentiation of the vegetative organs the order 
rivals the Fucaeew, and generally exceeds it in 
stature. Cryptostomata with septate paraphyses 
occur in Saccorhiza, Adenocystis, and Ulopteryx, while 
tufts of such paraphyses not within cryptostomata 
are found on the fronds of Alaria. 
The Thallus—The order has been divided by Mr. 
Setchell into three tribes, according to the methods 
by which the complexity of form of the adult plants 
is attained. The differences in question naturally 
arise at the intercalary growing-point, and the three 
types of growth are the Laminaria type, the Lessonia 
type, and the Alaria type. 
The Laminaria type, to which the genera Chorda, 
Saccorhiza, Agarum, Thalassiophyllum, Costaria, 
Cymathere, and Arthrothamnus conform, is charac- 
terised by unbranched fronds (except Thalassio- 
phyllum) and by a simple unmodified plane growing- 
point situated at the place where the stalk expands 
into the blade, with nothing in its appearance to the 
naked eye indicating the fact that here the stalk is 
