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. a 
