176 Collins and Howe: Species of Halymenia 



2 or 3 cm. in width. From Halymenia floridana, H. Gelinaria 

 differs in the much more gelatinous, often thicker, thallus, in the 

 less firm, obviously filamentous rather than parenchymatous or 

 subparenchymatous cortex, in the deliquescent outer walls of the 

 superficial cells, in the longer cells of the medullary filaments, 

 and in the comparatively rare and inconspicuous and differently 

 shaped medullary ganglia. In H. floridana the freely anastomos- 

 ing medullary ganglia are, with proper illumination or with 

 differential staining* the most conspicuous anatomical feature of 

 the thallus; their radiating branches are coarser than the ordinary 

 medullary filaments and the ganglionic system looks like a sort 

 of skeleton or framework about which the rest of the thallus has 

 been filled in. In H. Gelinaria, small stellate cells, with ordinary 

 unspecialized protoplasts are normal elements of the subcortex, 

 but larger specialized stellate ganglia of the medulla with re- 

 fringent protoplasts are rare or occasional and are not usually 

 obvious without a special search; their radiating branches are 

 commonly more slender than the ordinary medullary filaments 

 among which they make their way; these branches rarely anasto- 

 mose, commonly showing free ends, and they are, perhaps, rather 

 more suggestive of medullary rhizoids than parts of a primary 

 framework, yet they seem to differ from the medullary rhizoids 

 of the Florideae in general in being straighter and more rigid, 

 and in having denser more homogeneous refringent protoplasts. 

 Medullary ganglia of a somewhat similar sort are of occasional 

 occurrence in H. Floresia also. The difference between H. 

 Gelinaria and H. floridana as to the character of the cortex comes 

 out strongly when a section is made or even when a margin or a 

 fold of the surface is examined microscopically; in H. Gelinaria, 

 the dissolving away of the outer walls of the superficial cells 

 leaves these cells more or less isolated and separate, so that the 

 general surface appears minutely papillate, while in H. floridana 

 under the same conditions the general surface is covered by a firm 

 cuticle and is perfectly smooth. The cystocarps of H. floridana 

 and H. Gelinaria appear to be very similar in form, size, and 

 structure, but it is possible that an exhaustive study of the earlier 

 stages of their development might reveal differences as marked 



* See page 171. 



