HOW TO KNOW THE SEAWEEDS 



33a Cylindrical axes more or less densely clothed with slender, bristle- 

 like lateral branchlets. Fig. 55 Digenia simplex 



I 



mm 



Figure 55 



Fig. 55. Digenia simplex (Wulfen) C. Agardh 



A. An upper part of a plant of rather lax habit, X 0.8. B. A small 

 part of a single lateral, determinate branchlet to show the cortication, 

 X 80. Although it is difficult to observe the apical cell of main axes 

 because of the abundant lateral branchlets, the apical cells of the 

 determinate laterals are often readily observed. This is a common 

 tropical plant of Florida and the Gulf of Mexico to Texas. Under favor- 

 able conditions when the water is well protected the plants may be- 

 come luxuriantly developed and much-branched, up to 8 to 10 inches 

 high, while in rough, surfy locahties the plants are usually stubby, 

 dwarfish and httle-branched. They are commonly of unsightly appear- 

 ance because of multitudes of epiphytes which cover them. 



33b Axes not clothed with slender, hair-like lateral branchlets (but 

 note also Odonthalia iloccosa. step 179) 34 



54 



