70 



PLANT MORPHOLOGY 



gmm 



' ° " lyj ^.Ly. ' 



ti.ii4-j\'-i- 



m 



me 



® 



tm 



B 



Fig. 56. Sphacelaria, X200. A, tip of filament, showing large apical cell and segments 

 derived from it; B, slightlj' older portion of thallus, showing development of branches. 



3. Cutleriales 



The Cutleriales are a very small order including only Cutleria, with 3 

 species, and Zanardinia, with 1. Both genera occur in the Mediterranean 

 Sea, while Cutleria has been reported also from Florida, the West Indies, 

 and the Gulf of California. The Cutleriales are more advanced than the 

 two preceding orders, although apparently related to them. 



Cutleria. The best-known species of Cutleria is found in the warmer 

 parts of Europe. The plants grow just below the low-tide mark. Cut- 

 leria displays a heteromorphic alternation of generations, the gametophyte 

 and sporophyte being unlike \'egetatively. In fact, they are so different 

 in general appearance that, before they were known to belong to the same 

 Ufe history, they were placed in separate genera. The gametophyte was 

 called Cutleria and the sporophyte Aglaozonia. The sporophyte is a 

 small, flat, lobed disk several layers of cells in thickness and about 2 to 

 5 cm. in diameter (Fig. o7E). The lower side bears numerous rhizoids. 

 On the upper side are enormous numbers of elongated unicellular spo- 



