ALG 69 
including all the giant kelps, show only the simplest 
possible form of reproduction, ¢.e. purely non-sexual 
zodspores. Many of these larger kelps show an external 
differentiation which simulates closely the parts of the 
higher terrestrial plants. A definite axis, with lateral 
leaf-like outgrowths, has 
its base modified into a 
mass of firm root-like or- 
gans, forming a most 
efficient holdfast or an- 
chor, which, in some of 
the largest kelps, when 
torn away may carry 
with it a mass of rocks 
and shells weighing sev- 
eral hundred pounds. 
The leaves of the lar 
oe eae Fie. 18 (Fucacez).— A, a fragment of the 
kelps are often several common gulf-weed, Sargassum, show- 
. ing the definite stem and leaves, and 
metres in length, and the berry-like floats, v; B, the egg of 
the common rock-weed (Fucus vesi- 
although structur ally culosus), being fertilized by the minute 
they differ widely from bistate sparmatoraids, ©, 2 sug 
those of the higher 
plants, yet functionally they must be considered as 
equivalent to these. It is in these organs that the 
greater part of the chlorophyll-bearing cells are situ- 
ated. The peculiar floats or air-bladders found in these 
plants are formed by the accumulation of gases within 
certain parts of the plant, resulting in a distention of 
the thallus at these points, but the details of their 
development cannot be given here. 
While some of the forms, including the larger kelps, 
appear to possess only non-sexual zodspores, others, like 
