68 EVOLUTION OF PLANTS 
dition between these and the simplest types, like Ecto- 
carpus (Fig. 16). Among the most characteristic of 
Fie. 17.— A young plant of Nereocystis 
Lutkeana, one of the large kelps, 
much reduced, showing the holdfast, 
r, and the float, v, with the large 
leaves at its summit; the fully grown 
plant may reach a length of a hun- 
dred feet or more; B, the simple uni- 
locular sporangia, sp, and sterile 
ney or paraphyses, par, much mag- 
nified. 
these larger forms 
may be mentioned the 
great bladder-kelps of 
the Pacific (Macro- 
cystis, Nereocystis) 
(Fig. 17), and the 
smaller Laminarias of 
the Atlantic. Many 
of the larger kelps 
grow where they are 
exposed to the full 
force of the heavy 
surf, and this ac- 
counts for the tough, 
leathery consistency 
of many of them, and 
the powerful hold- 
fasts or roots. 
An examination of 
the whole class shows 
that within it there 
has been much such 
an evolution of the 
reproductive cells as 
we have seen in sev- 
eral groups of the 
green alge; but this 
is by no means paral- 
leled by the vegetative parts, as the largest, and, so far as 
the plant-body is concerned, the most specialized forms, 
