214 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



Fig. 54. 



Threads and cysts of Ckordaria divaricata. Magnified. From specimens 

 communicated by Dr. Harvey. 



3. DiCTYOTE^, Grev. 



Frond mostly flat, sometimes cylindrical ; surface reticulated. 

 Spores or cysts external, collected in little patches. 



199. We have here an assemblage of coriaceous or mem- 

 branaceous Algee, the surface of which is sprinkled with groups 

 of naked spores or spore-cysts. The endochrome is usually 

 entire, but sometimes it is quadripartite, and sometimes the 

 divisions are eight in number. In one of the genera only, 

 anything like antheridia has been observed, and there is reason 

 to beheve that in Cutleria at least the contained bodies may 

 possibly have the power of impregnation. The zoospores in 

 the quadripartite endochromes are very large, of a dark colour, 

 and have two lateral threads, while the bodies in the filiform 

 multiseptate antheridia, seated variously on the tufted threads, 

 are far more minute, pale, but with similarly situate appen- 

 dages (Fig. 52, a, b, c, d). A few species occur on our coasts, 

 and they are not more numerous on the coasts of North America; 

 several are found in the Mediterranean and other warmer seas, 

 and they are characteristic rather of tropical and sub-tropical 

 seas, where they obtain their maximum of development. 

 Padina Pavonia is common in the south of England, but 

 does not extend far north, and on the American coast it com- 



