232 ESSENTIALS OF BOTANY 
298. Discussion. — Fucus is a much more 
highly developed plant than any of the blue- 
green or green alge studied in the previous B 
sections. It has a complete cellular 
structure and there is considerable 
division of labor among the differ- 
ent parts of the plant. It has a 
special holdfast, air-bladders to 
serve as floats,! a tough midrib run- 
ning lengthwise of the branches and 
strengthening them, and expanded 
margins of the 
branches, afford- Fie. 162. Rockweed 
ing ample ana 
surface for A, antheridia borne on branch- 
ing hairs (x 160); B, three 
photosyn- sperms from the same 
thetic work. ‘* *8)- 
The outer layers of cells are espe- 
cially devoted to photosynthesis 
and the inner ones to storage of 
food material. The 
brown cell-contents 
contained in Fucus 
and other brown alge 
is highly efficient in 
photosynthesis. 
Fic. 163. Rockweed (Fucus). There is no asexual 
A, odgonium, its contents dividing into eight pe of reproduc- 
odspheres (X 160); B,an odsphere, escaped, tion in Fucus. Sexual 
surrounded by many sperms ( X 160). reproduction is ac- 
complished by the eggs and. sperms becoming forced out 
1 These are absent in some species (Fig. 161). 
