314 



NATURE 



{August 4, 1887 



been made upon the fruit of the Siphonea^ ; but the httle 

 that is known on this subject proves that great differences 

 exist in the fructification of these Algse. Thus the organs 

 of reproduction in Vauclieria differ from those of Botry- 

 dium, while those of the latter vary from those of 

 Bryopsis, Codium, Dasycladus, and Acetabularia. Of 

 many other genera observations are deficient or in various 

 respects uncertain and inconclusive. For interesting 

 general remarks on the fructification of the Siphoneje the 

 reader is referred to page 10, and for special details to the 

 observations on each genus and on the fruit of such of the 

 species as are best known. 



Setting aside the true characteristics of the fruit, it 

 becomes a question by what characters of the structure 

 the Siphoneae are to be distinguished from the Confervese 

 and Ulvaceee, and their affinities determined. In Dr. 

 Agardh's opinion these characters are to be found in the 

 filaments or utricles of the frond, being tubular, and not, 

 as in the Confervacese and Ulvaceae, consisting of sub- 

 divided cells. Good examples of the former are afforded 

 by Caulerpa and Valonia, whose fronds, roots, stems, 

 branches, and ramuli, though distinct, consist of a single 

 cell. These remarks are followed by observations on the 

 comparative structure in different genera and their 

 affinities with each other. 



With the exception of Vaucheria and Botrydium, says 

 Dr. Agardh, the Siphoneae inhabit the sea. This is 

 unquestionably the case as regards Botrydium, but it may 

 be asked whether it be quite true as to Vaucheria, several 

 of the British species of which are recorded by Dr. 

 Nordstedt ("Remarks on British Submarine Vaucherias," 

 Lund, 1886) as growing at the lowest tide-marks, and one 

 species {V.piloboloides, "probably in quite saltwater." The 

 greater number of the Siphoneae are natives of the warmer 

 seas, and are especially abundant on the shores of rocky 

 islands of which the principal constituent is lime. They 

 spread their fibrous roots among the sandy debris, and 

 are thus useful in holding together the particles of sand. 



Some of the Siphoneae have creeping stems, as have 

 the Caulerpeas. These plants, by extending the network 

 of their creeping stems and roots over the sand, seem 

 to exercise on the coast, within tide-marks, the same 

 functions as the Maram {Psaintna arenaria). This plant 

 grows on the coast of Norfolk, and is found so useful in 

 holding together the particles of sand, and thus aiding in 

 the formation of land and preventing the inroads of the 

 sea, that strict regulations are in force to prevent its 

 destruction. In the same manner as the Maram spreads 

 over the dry sands, the Caulerpete extend on the sea- 

 shore within tide-marks, and are thus uncovered at low 

 water. When the tide is out, they resemble green 

 meadows. The utility of these plants in protecting the 

 land was, a few years ago, unexpectedly proved in the 

 neighbourhood of Adelaide, South Australia. A farmer 

 suffered his sheep to stray upon the coast where the 

 Caulerpeae were exposed at low water. The sheep 

 devoured the Algee ; the sea consequently broke in and 

 established itself, and land was thus permanently lost. 

 Many species, as Halimeda and Penicillus, have roots 

 which are occasionally as large as small hens' eggs, 

 formed of innumerable branched fibres which penetrate 

 deeply into the sand. Some of the stipiform species emit 

 flagelliform creeping " propagula," from which spring new 



plants ; hence, observes Dr. Agardh, the Siphoneae may 

 be said to be social plants. Some Algas, as Anadyomene, 

 grow in shallow water exposed to the full influence of 

 light, while others, like Bryopsis, prefer deep water to 

 which light scarcely penetrates. 



Many, but not all, of the Algae belonging to the 

 Siphoneae have, like the Corallina family, the power of 

 absorbing lime from the water. Young plants are gene- 

 rally green, but the incrustation of lime, in certain 

 species, increases with age. In some genera it is entirely 

 absent, as in Codium ; in others it is extremely slight ; 

 while in some species of Halimeda the whole frond is 

 frequently cased with a hard coating of lime, and looks 

 like a gigantic frond of Corallina. 



The disposition of the families of which the Siphoneae 

 are composed must be attended with some difficulty until 

 the fruit is more perfectly known. In the interim Dr. 

 Agardh proposes the arrangement adopted in the work. 

 The group has been considerably enlarged, including as it 

 now does the Dasycladeae and Valoniaceae. With regard 

 to the former, the author observes that the Dasycladeae 

 are quite distinct from all the other genera, with their 

 verticillate stems and external sporangia ; hence he con- 

 siders that they undoubtedly form a natural family. The 

 fructification nevertheless varies in different genera. 



There appears no doubt as to the limits of the 

 Caulerpeae. These are set forth in the first part of the 

 present work (" Till Algernes Systematik"), and, although 

 some observations are still wanting as to the fructification, 

 the Caulerpeae form a very distinct family. 



The limits of the Valoniaceae are very difficult to 

 determine. In the form and size of their cells they for 

 the most part are very near the Caulerpes. They are 

 little more than ramulose prolifications ; hence the rami- 

 fication, although it is in some species more or less 

 obscured, may be said to have a common character. But 

 little is known of the fruit of these plants. In some 

 genera the structure varies from that of the other 

 Valonite, and approaches near to that of Ulva, as may be 

 seen in Dictyosphaeria and Anadyomene. 



Among the remaining genera are some whose fronds 

 consist almost entirely of compound tubes incrusted 

 with lime. In these the normal ramification is di-tricho- 

 tomous, but in Bryopsis and Codium— which, however, are 

 not coated with lime— it may be said to be pinnate. Of 

 the fructification of these plants few observations are 

 recorded. In Udotea Desfontainsii and Halivieda tuna, 1 

 true sporangia have been observed. Both belong to the I 

 Udoteaceae. Whether the Spongodieae, with their quasi- 

 composite fronds, and the Bryopsideae, with their free^ 

 filaments, should be separated from each other, or unit^ 

 into one family, may be subject for consideration. 



Vaucheria and Botrydium are not treated in tl 

 present work : neither does Dr. Agardh know to whi^ 

 family of the Siphoneae they should be attached. 



The whole group, in which the Dasycladeae a« 

 Valoniaceae are now included, is thus arranged by 

 Agardh : — 



I. Bryopside^. 



(i) Bryopsis; (2)? Derbesia. 



II. SPONGODIE.E. 



(3) Codium, ? ? Cladothele. 



