196 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



nised only by their calcareous nature. Some of them are 

 mere amorphous crusts on pebbles or sea-weeds, increasing 

 like the lichens, which they resemble, from a common centre. 

 Others are of stony hardness, lobed and branched, like the 

 clavate Fungi, and resemble true corals ; others are filiform 

 and repeatedly articulate, the joints often assuming an obovate 

 form, while in others they are flabelliform and approach in 

 character such Chlorosperms as Haliriieda. It is not, how- 

 ever, every part of the plant which appropriates calcareous 

 matter; in many there are internodes varying greatly in length, 

 which are either entirely free, or ornamented with calcareous 

 plates. It is through these free areolee, probably, that water is 

 imbibed for the purposes of nutrition. It is to be observed that 

 what are here called spore-threads, may also be regarded as 

 tetraspores ; but I think that Dr. Harvey is quite right in his 

 notion as to their being of the same nature with the spore - 

 threads in the foregoing division, inasmuch as they are con- 

 tained in distinct conceptacles. The subject is not, however, 

 without diflSculties, and at present has scarcely been suffi- 

 ciently studied to lead to any positive results. Kiitzing figures, 

 in C. officinalis, spores very different from the usual tetra- 

 spores, whether rightly called so or not, and indeed almost 

 exactly like those of Alsidium.* Dr. Harvey figures three 

 forms of fruit in Corallina squamMa, representing respectively 

 the fructification of Jania, Amphiroa, and Corallina, which 

 again perplexes the subject, and makes one doubtful of the 

 goodness of the characters on which the genera are founded. 

 As in several other calcareous Algse, a thin pellicle separates 

 under the action of hydrochloric acid, marked with the hexa- 

 gonal impressions of the external cells (Fig. 48, d). 



173. The genus Amphiroa, which exhibits many of the more 

 singular forms, though not found on our coasts, occurs under 

 several species on both coasts of North America, on the east ex- 

 tending as high as Unalaschka and Sitcha. On our own coasts 

 we have Corallina officinalis abundant everywhere, and reach- 

 ing far higher northwards than Jania. The crustaceous species, 

 also, whether on leaves or pebbles, or lying free at great depths 

 * At least in A. tenuissimum, Kiitz,, wMcli is Chondria tenuissima, Ag. 



