62 
Barber . — On the Structure and 
There appears then to be a distinct aim at rendering the 
flat stalk as rigid as possible, and thus more securely to bear 
the huge frond attached to it. Finally, the flattened upper 
part of the stalk just below the lamina is more readily bent 
than other parts, and may act as a hinge. 
It will be seen from the figures that, in the early stages, the 
stalk of L. bidbosa is cylindrical ; and this may be regarded 
as evidence of the descent of the species from a form more 
nearly resembling those other Laminarias, in which the stalk 
is still rounded. There is a great amount of morphological 
differentiation in this species, and it appears to represent a 
specialized type when compared with the other members of 
the genus. It is not easy, however, to assign a reason for the 
departure of the stalk from its rounded form. Greater strength 
might be aimed at ; but any amount of strength may be ob- 
tained by the secondary thickening found in round-stalked 
Laminarias. A tendency towards the increase of the assimi- 
lating surface, so apparent in the huge development of the 
lamina, may have extended its influence to the stalk as well. 
Or, lastly, the tendency of the sporangia towards the ‘ roots,’ 
in this species as in Alaria , might be facilitated by a flattened 
and subsequently folded stalk. 
There seems in this plant, as in Alaria , to be incipient separation of the 
assimilating and reproductive regions which are still united in other Laminarias. It 
is interesting to contrast these plants with those growing on land. In the latter the 
spores are usually non-motile, and are dependent on various external influences for 
their dissemination. Their reproductive organs are therefore situated in the most 
exposed situations at the summit of the stalk or at the end of a branch. Here, 
however, the spores are motile, and everywhere around them is the medium in 
which they may disperse themselves ; accordingly it is rather of advantage than 
otherwise that the sporangia are developed nearer the base of the plant. The 
sporangia are thus more sure of being undisturbed, and the spores are nearer to the 
substrata, to which the young plants become fixed. 
Although we cannot state that the flattened form of the 
stalk is due to the necessity of supporting the huge leaf, we 
may yet safely conclude that the various other attempts at 
rigidity, and secure foothold, were caused by the great develop- 
ment of the lamina. An enormous assimilating surface has 
been formed, and it must be supported. The plant appears to 
