166 BOTANY. 



elongates below into root-like processes, which serve to 

 hold fast the new plant ( F, IV). 



Practical Studies. — (a) Secure specimens of Rockweeds, fresh, alco- 

 tolic, or dry. Fresh ones may easily be found along the beach of the 

 ocean after a storm. Alcoholic and dry specimens can easily be pro- 

 cured by purchase or exchange. Make thin cross-sections through 

 the conceptacles in the thickened ends of the branchlets. When 

 mounted in water, even the sections from the dry specimens will fre- 

 quently show the sexual organs quite well. It must be remembered 

 that some species are dioecious, i.e., have the antherids on one plant 

 and the oogones on another. 



(6) Make very thin cross and longitudinal sections of different 

 portions of the plant-body, and study the tissues. Note particularly 

 the boundary tissue (c;iidermis), and the cells constituting the mid- 

 ribs and harder portions of the stems and leaves. 



(c) The following key to the genera of American Fucaceae 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, constitut- 

 ing the so-called Sargasso Sea. Its proper home is in 

 the West Indian region, where it grows attached to 

 rocks. 



3. Leaves spirally inserted, bearing air-bladders on their 

 blades (southern) ..Turbinaria. 



3. Leaves 2-ranked, bearing air-bladders on their petioles 



(Western) Phyllospora. 



4. Plant pinnatifid ; air-bladders several-celled, terminal on 



the branchlets (western) Halidrys. 



5. Plant dichotomous, the parts flat and provided with a 



midrib (both coasts) 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) Ascophyllum. 



7. Plant much branched, bushy, the branches filiform (West- 



ern) , . .Cystoseira. 



II. Plant reduced to a top-shaped or cup-shaped vesicle (doubtfully 



American) Himanthalia. 



Systematic Literature. — Farlow, Marine Algse of New England, 

 99-104. 



