132 CRYPTONEMIACE.E. 



substance, but always composed in great measure, or often 

 altogether, of filiform strings of cells, or articulated fila- 

 ments. The cells or articulations of these filaments are 

 either long and cylindrical, or more and more ellipsoidal or 

 spherical, in which latter case the filaments become monili- 

 form. In the genera of simplest structure (Crouania, Du- 

 dresnaia] the substance of the frond is loosely gelatinous 

 and the threads are separated from each other by interposed 

 colourless gelatine or mucus. The frond in such cases is 

 highly elastic. It appears to the naked eye to be inarticulate, 

 but when placed under the microscope is resolved into bun- 

 dles of coloured filaments, radiating from a transparent bed. 

 In the next advance of structure (as in Catenella and Haly- 

 menia] the filaments composing the outer coat of the frond 

 are closely compacted and formed into a sort of membrane, 

 while those belonging to the axis form a lax net-work, sur- 

 rounded by mucus. In still more perfect genera (Gigartina, 

 Gelidium, &c.) the substance becomes more and more firm ; 

 the cells of the axis are closely entwined, and anastomosing, 

 and those of the periphery very minute, and cohere strongly 

 by their sides. Thus at last we have structures formed as 

 close and hard as those built up of polygonal cells. But the 

 loose and fibrous structure characteristic of Cryptonemiaceas 

 becomes apparent in such plants as the Gigartinae when the 

 frond is allowed to soak for some time in fresh water, or when 

 plunged for an instant into boiling water. A piece of Gigar- 

 tina acicularis thus treated will be changed into a body 

 having the appearance, under the microscope, of a Dudres- 

 naia or Nemaleon. The habit of the loosely gelatinous gene- 

 ra is generally filiform, and branching. That of more perfect 

 genera often shows a disposition to form leafy membranes, 

 and in the most perfect the leafy branches have imperfect 

 midribs, as is the case in Suhria and some species of Gelidi- 

 um, and Phyllophora. Ginannia is remarkable for having 

 a cylindrical frond, with a dense rib-like axis, surrounded by 

 a space of much laxer structure intervening between the 

 axis and true periphery: the axis is much more strongly 

 developed in some specimens than in others, and often looks 

 especially in dried specimens of broad fronds, like a true 

 midrib. The leaf-like fronds in this order are rarely deli- 

 cately membranaceous. They are more frequently thick and 

 fleshy, as in our Iridaa, and in many exotic species of Gi- 

 yartina with the external habit of Iridaa. There is nearly 

 as much variety in the appearance and disposition of the 



