TYPES OF CRYPTOGAMS; THALLOPHYTES 219 
THE STUDY OF ROCKWEED! 
278. Occurrence. — The common rockweed is abundant everywhere 
on rocks, between high and low tide, on the New England coast and 
southward. 
279. The Frond. — A plant of rock- 
weed consists mostly of a growth which 
is somewhat leaf-like, but, in fact, stem 
and leaf are not separately developed, 
and the growth is therefore called a 
thallus. This combined stem and leaf 
has many flat leathery branches which 
are buoyed up in the water by air- 
bladders. Cut one of the bladders 
open and note its form and appearance. 
Note whether they occur singly or how 
grouped. Note the prominent midrib 
running throughout the middle of each 
branch. Examine the swollen tips of 
some of the branches and note their 
peculiarities. Sketch a portion of a 
frond to show the characteristics so far 
noted. 
280. Reproduction. — Cut across 
through the middle of one of the swollen 
fruiting tips. Note the fruiting papille 
(conceptacles) as they appear in this see- 
tion, and make a simple sketch to show 
their position. 
Select some plants with brighter- 
colored tips and some less bright, if any 
difference can be detected. After mak- 
ing the microscopic examination which 
follows, note what correspondence of 
Fic. 154. Part of Thallus of 
a Rockweed (Fucus platy- 
carpus). (Natural size.) 
The two uppermost branchlets 
are fertile. 
structure with color has been observed. Cut very thin sections 
through fruiting tips from different plants, keeping those from each 
1 Fucus vesiculosus is the most available species. Others may be substituted. 
