Archer — On Apoiliecia in Algce. 91 



But does it not appear somewhat inconsistent when Bornet, in describ- 

 ing his ZicIie7iosj)k(en'a Lenormandi, makes use of the folio wing lan<?uage 

 in the generic character: — " Thallus tenellus, ramosus, fruticulosus, 

 fere onmino stigonematoideus, basi corticatus ; " and as descriptive of 

 the specific characters — ' ' Thallus fusco-ciger, tomentoso-intricatus 

 (altitudo yix 2 millim.), ramulis divaricatis subsecundis " ? For, in 

 fact, these words simply describe the thallus of &irosiplwn divaricatus, 

 Kiitz., which alga forms the host-plant for the peculiar lichenal para- 

 site in question. But when he goes on to describe the apothecia, the 

 thecae, the spermogonia, the spores, he is giving the characters of the 

 latter, which is the real " new species." In accordance with the new 

 theory, besides the hyphte, this has no thallus of its o\vn ; the hyphse 

 merely push into the thallus of the Sirosiphon, scarcely distorting it or 

 causing any outward alteration, beyond the occasionally exserted apo- 

 thecia. If it were possible — and there is seemingly no great reason to 

 the eontraiy — that the spores of this self-same LicTienof^pTiaria Lenor- 

 mandi should afterwards grow upon and into another species of Sirosi- 

 phon, or, say even into a Scytonema, then some of the " specific charac- 

 ters " as given, nay, even probably some of the "generic," would 

 disappear and others take their place. It is to be granted, indeed, that 

 on the new theory, when a Nostoc becomes invaded by the parasite 

 which converts it into a Collema, a very considerable alteration is pro- 

 duced on even the outward aspect of the JVostoc ; instead of a rounded, 

 lobed, " blobby," and soft lump, it becomes more or less foliaeeous, 

 less watery, and more subdivided ; but it is the alga all the time which 

 submits to this alteration : the true lichen is inside, only evinciag itself 

 externally by its apothecia and by its action on the alga (like a gall 

 causing even greater modifications on a higher plant), inciting those 

 changes of external aspect, whilst it is at the same time making use of 

 the assimilating power of the alga to do for it what it cannot do by 

 itself. 



There can be little doubt but that amongst these Scytonematous and 

 Sirosiphonaceous algae quite distinct forms occur ; but, on the other 

 hand, there can be almost as little doubt but that Kiitzing has vastly 

 over-enumerated them — that many of his so-called species are not dis- 

 tinguishable. ]S^ow, it is hard to conceive that one and the same para- 

 site would care veiy much ivhich of forms so closely resembling it in- 

 vaded in order to piirsue its course of life. Sirosiphon divaricatus 

 seems not to differ much trom S. alpinus ; it is more fruticulose, the 

 cells in the central stems seem to occur in more than double series : 

 what very perceptible barrier is there to the supposition that the para- 

 site, which invades the former to form LiclienosphcBria Lenormandi, 

 Bornet, might not at another time invade the latter ? Would it not 

 then fructify in the same way, show spores alike, &c. ? But the para- 

 site which does really invade the latter is not the same, as the figure 

 herewith will show, not to speak of the paraphyses, so prominent 

 a feature in the latter, being absent in Bomet's plant. Are these Scy- 

 tonemicolous and Sirosiphonicolous parasites, then, so extremely parti- 

 cular in their choice ? 



