262 University of California Puhlications in Botany [Vol. 8 



to refer observations as to the behavior of the plants referred to them. 

 Cultural studies are needed and, although possibly difficult, may, even 

 for certain more readily grown forms, yield results of extended 

 application. 



From our own experience, we feel convinced that general habit 

 and size do not, as a rule, vary within extensive limits in the adults 

 of the same species, while the details of cell structure are fairly 

 uniform for any particular part of an adult plant within the species. 

 Both habit and cell structure are sufficiently variable among the 

 species, however, to afford intelligible diagnostic characters. 



Key to the Species 



1. Frond lanceolate with tubular stipe 1. U. Linza (p. 262) 



1. Frond variously shaped, stipe when present, solid 2 



2. Cells square, or nearly so, in cross section 3 



2. Cells distinctly vertically elongated in cross section 6 



3. Frond seldom over 2 cm. high 2. U. califomica (p. 264) 



3. Frond usually over 2 cm. high 4 



4. Frond narrowly lanceolate 3. U. angusta (p. 264) 



4. Frond broad in proportion to length 5 



5. Frond attached, orbicular or ovate, often deeply split 4. U. Lactuca (p. 265) 



5. Frond usually soon free, ample and exapnded 5. U. latissima (p. 266) 



6. Frond broad in proportion to height 7 



6. Frond narrow in proportion to height or with long, narrow laciniae 9 



7. Frond apparently regularly and abundantly perforated. ...6. U. fenestrata (p. 267) 



7. Frond not perforate or occasionally showing a few irregular holes 8 



8. Frond ample, usually with deep ruffled margins 7. U. expansa (p. 268) 



8. Frond moderate, deeply lobed, with slightly ruffled or plane margins 



8. U. lobata (p. 268) 



8. Frond short ovate, plane, usually deeply split 9. U. rigida (p. 269) 



9. Frond long, usually simple, more or less ruffled 10. U. stenophylla (p. 271) 



9. Frond very short, simple, plane 11. U. vexata (p. 271) 



9. Frond deeply divided into long, narrow, crisped laciniae 10 



10. Laciniae borne on a short, broad, basal portion, not dentate below 



12. U. dactylifera (p. 272) 



10. Laciniae split to the very base, dentate below 13. U. taeniata (p. 273) 



1. Ulva Linza L. 



Plate 12, figs. 1-4 



Frond lanceolate or linear-lanceolate, simple, 1-5 dm. long, 1-20 

 cm. broad; stipe longer or shorter, hollow; upper part of the frond 

 flat, the two layers of cells completely united or remaining free along 

 the whole or part of the margins, which are plane or more or less 

 undulate; membrane 25-70/* thick; cells usually vertically elongated 

 in section, up to twice as high as broad. 



