MORPHOLOGY 
being most abundant in northern latitudes. In the North Atlantic the 
large forms are chiefly species of the Laminaria type, the body resembling 
a huge leathery and stalked leaf blade sometimes 9 to 10 m. long, an- 
chored by a rootlike holdfast (fig. 123). The most remarkable forms, 
with variously arranged blades, occur on the Pacific coast, among 
them being Macrocystis 
(giant kelp), whose huge 
bulk sometimes extends 
200 to 275 m. (fig. 124); 
Nereocystis (bladder 
kelp), with long flexible 
stem (reaching 60 m.) 
that swells at the end into 
a large globular float to 
which are attached large 
blades (fig. 125) ; Les- 
sonia, with a dichoto- 
mously branching stem 
like a tree trunk; and 
Postelsia or sea palm, 
whose name suggests its 
habit (fig. 126). 
The bodies are differ- 
entiated into blade, stipe 
(sometimes extremely 
long), and holdfast. The 
holdfast often takes the 
appearance of an exces- 
sively branching and 
FlG. 126. Postelsia (sea palm) ; showing numerous very tough root system, 
blades from the massive stipe, and the system of hold- \y\ft j^ sno uld not be con- 
fasts. 
fused with roots in either 
structure or function. There is also often a marked differentiation 
of the cells into distinct tissues. For example, a section of the stipe of 
Nereocystis shows an outer pigment-bearing zone (cortex), a zone of 
storage cells, and a pith region (medulla) of loosely woven elongated 
cells. Although often very large and complex in form and tissues, the 
kelps, so far as known, are very simple in their reproductive methods. 
The gametangia occur in dense masses on certain portions of the ordinary 
