OOPHYTA. 147 
(6) Make very thin cross and longitudinal sections of different por- 
tions of the plant-body, and study the tissues. Note particularly the 
boundary tissue (epidermis), and the cells constituting the midribs 
and harder portions of the stems and leaves. 
(c) The following key to the genera of American Fucacee will be 
helpful in their study. 
I. Plant branched: 
1, Leafy; air-bladders stalked, separate......... Sargassum. 
In addition to half a dozen species of both coasts, the 
Gulfweed (Sargassum bacciferum) may be mentioned, 
which floats in great quantity in mid-Atlantic, consti- 
tuting the so-called Sargasso Sea. Its proper home is in 
the West Indian region, where it grows attached to rocks. 
2. Leaves spirally inserted, bearing air-bladders on their 
blades (Southern). .......... cece eee cence ee Turbinaria. 
3. Leaves 2-ranked, bearing air-bladders on their petioles 
(OV CS CET I) ayes crassrepedarecntanareversrelacetatevareriesciaren cies Phyllospora. 
4, Plant pinnatifid; air-bladders several celled, terminal on 
the branchlets (Western)..............6 .....Halidrys. 
5. Plant dichotomous, the parts flat and provided with a mid- 
Tib (both coasts) ,« cccese sons vawd cean sare sees Fucus. 
This contains the proper Rockweeds of the seaside. 
Eight species occur in the United States, 
6. Plant irregularly dichotomous, the linear parts destitute 
of a midrib (Eastern). .............0 0006 Ascophyllum, 
%. Plant much-branched, bushy, the branches filiform (West- 
101) Cerne ee eerie emcee ee Cystoseira. 
II. Plant reduced to a top-shaped or cup-shaped vesicle (doubt- 
fully American) ps .:6:¢00cieaeeisieeeoaneecres Himanthalia. 
(2) The filamentous odphytes may be preserved for herbarium 
specimens by floating out as described on page 129 (j). The Mildews 
and White Rusts may be preserved by simply drying the affected 
leaves and stems (of the hosts) under pressure. : 
(¢) Preserve specimens in weak alcohol for future study. 
