INTRODUCTION TO CRYPTOGAMIC BOTANY. 185 



spores had fallen, and before cell-division had taken place, it 

 was not possible to distinguish them from true forms of the 

 present division. How far the division may in the end prove 

 tenable it is scarcely possible to surmise at present. There 

 will always be exceptions in any arrangement which may be 

 devised, be our knowledge extensive as it may. 



160. The number of distinct divisions and genera, and the 

 variety of forms, are very large, and we have here again species 

 remarkable for the quantity of calcareous matter which they 

 appropriate, even more so than those which were described 

 amongst Chlorosperms, many of which occur on our own coasts 

 as well as in warmer seas. The filiform species are numerous, 

 and some of them extremely beautiful, while many of the 

 membranous species are remarkable for the delicacy of their 

 fronds, or the symmetry of their composition. The regular 

 net-work of some of these Algae is as exquisite as that which 

 we have seen lately amongst Hydrodidyce ; and amongst the 

 membranous and sub-cartilaginous groups there is cancellated 

 work of the most surprising beauty. Some of these more 

 curious forms are confined within narrow geographical limits. 

 A few of the filiform species are habitants of brackish waters, 

 and in the tropics ascend rapid torrents on the coasts. 



5. Wrangeliace.e, Harv. {Wrangeliece, J. Ag.) 

 Threads filiform, articulated, sometimes partially coated 

 with cells. Nucleus surrounded by a whorl of byssoid 

 branclilets, and composed of radiating pyriform spores, arising 

 from the endochromes of the terminal cells. (Fig. 45, c.) 



1 61. These differ from other Desmiospermew in the exposed 

 involucrate nuclei. The habit is that of Callithaonnion, and, 

 like many species of that genus, they consist of a central thread, 

 coated more or less with smaller ones, sometimes disposed so as to 

 form the most elegant lacework ; in some, however, there are no 

 external cells or filaments, as in W. 'multijida. There is but one 

 genus, unless Naccaria be included, consisting of several species, 

 the greater part of which belong to the southern seas, while the 

 original one is a well-known native of our coasts. As regards 

 the tetraspores, the resemblance between this genus and Calli- 

 thamnion is complete, but there is no resemblance between the 



