Biblii xjrapli I'ra I XoficM. 131 



had been preoccupied in the Fiinfji, a reason whicli woukl not 

 now be considered surticieiit. Dr. Jlnbenhorst's definition telk tlie 

 true tale of its origin, " Pohjcystis thallo golutinoso, initio solido, 

 cetate provecta chithrato." It is, in fact, nothing more than a Poh/- 

 cystis the gelatine of which has become ruptured and perforated as 

 it has advancted in age. Of Merlsmopadia it may be reniaked that 

 it is with dithculty, if at all, to be distinguitshed from Sarcina *; 

 and if Sarcina (as some good authorities consider) is in reality not 

 an alga but a fungus, the validity of the genus may not unreason- 

 ably be questioned. With regard to Oncohyrsa it appears (we hare 

 not the work to refer to) to have been placed by Meneghini 

 amongst the Nostochinece ; and if this be correct, the genus can 

 hardly be supported after the observations of many past years 

 tending to show the connexion between Nostoc and the Collema- 

 ceous lichens. 



It would be going into too much detail to discuss at any length 

 the other five families of Dr. llabenhoi-st's rhycochromophycea'. 

 Doubts may be entertained whether many (if any) of the genera 

 of the Oscillariacece are autonomous, but they may reasonably be 

 retained here in the absence of indications of closer affinities eLse- 

 whcre. AVith n-gard to one of the genera, viz. Lyayhya, it has 

 been stated that it does not oscillate, at least when in long fila- 

 ments, wliich raises a doubt whether its proper position (assuming 

 it be a good genus) is with the OsciUariacec. Dr. Hicks has 

 suggested (Micr. Journ. n. s. vol. i. p. 164) that Lynyhya imiralis, 

 Schizoyomum, and Prasiola are but different stages of the same 

 organism ; but it is doubtful how far this view can be supported ; 

 for the two latter are chlorojjhyUaceous Alga;, which would seem to 

 render improbable any close connexion between them and Lynyhya, 

 which is phycochi-omaceous f. 



With regard to the Xosfochacere, the discussions which have 

 taken place as to their nature and affinities would fill a volume. 

 It was long since suggested that most if not all of the plants 

 usually placed in this family are only conditions of gelatinous 

 lichens — an opinion which is now gaining ground, notwithstanding 

 Mr. Berkeley's high authority on the other side, who says, in his 

 ' Introduction to Cryptogamic Botany ' (p. 141), that he cannot sub- 

 scribe to this doctrine. Xylander is of opinion that the Nostoc of 

 modem algologists, in part at least, if not entirely, may be re- 

 garded as the initial or metamorphic states of the CoUemata ; and 

 he even goes further, and considers that he has added to the lichens 

 various Scytoneniata and Sirosiphones, such as Synalissa picina, 

 is. melodermia, Scc.X 



Dr. De Bary suggests a singular alternative theory, which is 



• In the ' Botanische Zeitung ' for January 10, 1868, Ilallier states 

 that Sarcina dilfers from Meriamopcedia in its mode of di\-ision. 



t -"^ee some remarks by Mr. Archer in the Proc. Nat. Hist Soc. of 

 Dublin, vol. iv. p. 273. 



t See ' Notuhe Lichenolopncaj,' translated by Leighton in Ann. & Mag. 

 Nat. Hist, fur November 1808. 



