130 Bibliographical Notices, 



to very strong currents : Catenella, Polysiphonia ohscura, Chondrus, 

 Griffithsice and Gelidium ustulatum inhabit spots almost emersed or 

 sprinkled only with the spray; Rhytiphlecea tinctoria, in company with 

 a variety of Cystoseira abrotanifolia, is found in ditches ; Nemalion, 

 many forms of Gelidium corneum, Hypncca musciformis, Gigartina aci- 

 cularis, &c. prefer such parts of high- water level as are exposed to 

 waves ; Cystoseira amentacea covers in profusion the more submerged 

 rocks ; most of the Callithamnia, Griffithsice, Rhodomenia palmetto,, 

 Peyssonellia, Chondrus norvegicus, and forms of Gelidium corneum 

 inhabit the higher but more hidden rocks ; Phyllophora nervosa and 

 Ph. Heredia, with Ph. coronopifolius, adorn those which are concealed 

 but more deeply covered. Sphcer.Lactuca an&Chondria uvaria, withFa- 

 lonia utricularis, are often found in little hollows amongst sponges. 



Agardh considers the Alga? as constituting a distinct class, which 

 he divides into Zoospermece, Floridece and Fucoidece, which answer 

 nearly to Chlorospermei, Rhodospermei and Melanospermei of Harvey. 

 To these must be added Diatomacece, which however are not included 

 in the present enumeration ; nor are the Corallines and Halimedece, 

 of which Decaisne proposes shortly to gjve a monograph, than which 

 there are few greater desiderata in cryptogamic botany. 



Decaisne's main divisions in his ' Plantes Arab./ published in the 

 second volume of the ■ Archives du Museum d'Histoire Naturelle,' and 

 in the numbers for May and June of the present year of ■ Annales des 

 Sciences Naturelles,' correspond closely with those of Agardh, though 

 he makes one more division, Synsporece, to include Zygnema and its 

 allies, which are classed by Agardh with the Zoospermece. His Zoo- 

 spores, Aplosporece and Choristosporece accord closely with Agardh's 

 Zoospermece, Fucoidece and Floridece. Some genera, however, in- 

 cluded by Agardh in his first division, as Vaucheria, Codium and 

 Spongodium, are classed by Decaisne in his Aplosporece. 



It is scarcely possible, without entering into the subject at great 

 length, to give a sketch of their respective views and systems, espe- 

 cially as, notwithstanding the great similarity in the general result, 

 there are many points of controversy between the authors which at 

 present can scarcely be regarded as settled on firm grounds, and ano- 

 malies of structure unsatisfactorily explained or unnoticed*. We 

 must therefore content ourselves with very strongly recommending 

 all who take an interest in Algology to study the memoirs them- 

 selves, which will afford ample matter for reflectionf. Palmellece and 



* In Sphceroplea crispa, which is perhaps better referred to the genus 

 Lyngbya, there being no other essential difference than the ultimate globular 

 form of the concentrated masses of the green matter with which the joints 

 are filled, a very curious phenomenon occurs. The masses, which appear to 

 be as truly a form of fructification as the conyocysta of Aplosporece, being 

 surrounded by their own especial hyaline coat, as is also the case in Lyngbya 

 speciosa and Lyngbya Carmichaeliana, after a certain time break up again 

 into Zoosperms endowed with the most lively motion. Other equally ano- 

 malous facts occur which can scarcely be at present referred with certainty 

 to given types. 



t Decaisne, who has very deeply studied the subject, has referred with 

 great ingenuity the different forms of fructification to distinct types. He 



