INTRODUCTION TO CRYPTOGAMIC BOTANY. 181 



nucleus (Fig. 44, b), Loth of which are united by Harvey 

 for the very sufficient reason that the difference is one only 

 of degree, while there is the most intimate relation in structure 

 and habit. 



156. The numerous genera, of which thirty-five are proposed 

 l>y Agardh in his most recent general work on Alga?, are dis- 

 persed through all regions, though, perhaps, more common in 

 tlie northern hemisphere. Many are inhabitants of the warmer 

 seas, and we have several representatives in Britain. Twenty- 

 four genera, at least, occur on the east coast of North Ame- 

 rica. Stenogramma, which has been found on our extreme 

 southern coasts, occurs in California and Florida, in addition 

 to Spain, as far as Cadiz, and is very fine and abundant in 

 New Zealand. It is remarkable for the disposition of the nuclei 

 on each side of the central nerve, exactly after the fashion of 

 some ferns. Phyllophora, Oymnogongrus, Ahnfeltia, Cysto- 

 clonium, Callophyllis, Kallymenia, Oigartina, Iridcea, Ohon- 

 drus, Halymenia, Furcellaria, Chrysymenia, Grateloupia, 

 Catenella, Gloeosi2)ho7iia, have all representatives on our 

 coasts. The various species of Chondrus supply the greater part 

 of the Carrageen of commerce. One of the most beautiful of 

 seaweeds is Gonstantinea rosa marina, two of the species of 

 which genus occiu: in Kamschatcha, or other high latitudes, 

 while the third is found in the Mediterranean. The stem is 

 sometimes a foot and a half high, fixed to stones or shells, and 

 branched from the base ; the branches ai'e flexuous, round, and 

 naked, 1-2 lines thick ; horny when dry, annulated ; rings 2-3 

 lines distant. Towards the top of the stem and branches are 

 a number of whorled laminae, the terminal ones being peltate ; 

 the whole bearing some resemblance to an expanded rose. As 

 the lower laminaj grow old, they fall off and leave rings upon the 

 stem. The ultimate fronds rarely remain orbicular and entire. 

 The central one is about two inches in diameter, and divided 

 into from 3-6 obovate spathulate lobes.* Gonstantinea Sit- 

 chensis is a larger species, the solitary terminal orbicular 

 lamina attaining a diameter of from four to six inches. Ghy- 



* J. Agardh, 8p. Alg., vol. 2, p. 295. 



