92 Proceedings of the Royal Iriah Academy. 



See again the two Scytonemata, resembKng in themselves so much 

 and yet with " parasites " so distinct ; the spores could not be con- 

 founded for a moment (see figs. 1, 2, and fig. 8). Again, see the 

 great resemblance (but certainly not identity) between the spores in 

 the second Sctjtomma and in Sirosiphon imhinatus, algae mutually 

 sufficiently unlike (see Figs 8 and 23). 



It might again be asked whilst the new theory is, as it were, on 

 its trial, at what period of the life of the Scytonema or Sirosiphon does 

 it become invaded by the parasite ? At what part of the thallus does 

 it make its entry ? It must be near the base, or at least not very high 

 up, for the hypha is found growing pretty nearly ji?flr«'j9«ssi< with the 

 growth of a branch of the alga, and in the same general direction. 

 But what is to prevent the hypha growing in the opposite direction ? 

 Might it not sometimes enter near the apex and grow backwards ? 

 Might we not expect sometimes to find hyphae sticking out from 

 broken-up or distorted examples of these algae, and then revealing 

 themselves (without the whole mass being boiled in potash) whilst on 

 their way to invade other examples of qiiite the same alga ? Or must 

 the hypha appertaining to a particular plant have had its commence- 

 ment from a spore which found its way to and alighted somewhere ex- 

 ternally upon the particular Scytonema or Sirosiphon ? 



The account given by Itzigsohn of Ephehella * is incomplete ; he 

 met with apothecia in his species of " Scytonema,'''' containing asci, but 

 they had not as yet developed spoi'cs. The plant he had in view may 

 certainly be said to be quite distinct from Scytonema myochroiis. It is 

 probable the fructification would also have been seen, if fully mature, 

 to have been also specifically different. So also are my two forms, both 

 in thallus and fructification. These, proceeding on the new theory, 

 would, perhaps, be relegated as " new lichens" to Ephelella, Itzigsohn, 

 or to Gonionema, Nylander ; but neither is identical with Gonionema 

 velutinum, Nyl. (of which I have seen examples in the late Admiral 

 Jones's Herbarium), either as regards thallus or spores. The three 

 other forms would probably be referred as "new species" to the 

 "lichenous" genus Spilonem.a, or that referred to Sirosiphon pidvinatus, 

 wanting paraphyses, might possibly be relegated to LiclienosphcBria. 



An experimental decision of the " gonidia-question," so far as it 

 relates to these Scytoncmatous and Sirosiphonaceous fonns, is sur- 

 rounded by not a few practical difficulties. A sowing of spores upon 

 the algae (as Eeess did with Nostoc) in a natural condition could only be 

 carried out by an observer residing in or close to the subalpine situ- 

 ations where these plants flourish, as they could not be "cultivated" else- 

 where. In order to obtain the spores he would further have, very 

 probably, a troublesome preliminary search, and, on the other hand, 

 there would hardly be a certainty of the plants selected for inoculation 

 being themselves previously destitute of hyphae or apothecia. Of course 

 small portions from various places in a tuft of any given alga could be 



* Itzigsohn, in " Hedwigia," 1857, p. 123. 



