( xxix ) 



nor less than describing tlie characters of " Sirosiphon divaricatiis, 

 Kiitz." (the plant invaded by the "parasite"); but when he goes 

 on to describe the apothecia, the paraphyses, the spermogonia, the 

 spores, he is giving the characters of the parasite aad the real ' ' new 

 species." 



There can be little donbt but that 'amongst these Scytonematous 

 and Sirosiphonaceous Algse quite truly distinct forms occur, but, 

 on the other hand, there can be almost as little doubt but that 

 Kiitzing has very greatly overrated their number. ISTow it is hard to 

 conceive that one and the sane parasite would care very much which 

 of closely-resembling forms it invaded in order to pursue its course of 

 life. Siromplion divaricatus seems not to differ much from .S*. alpinus 

 (one of those now brought forward with apothecia) ; now what very 

 perceptible barrier is there to the supposition that the parasite which 

 invades the former to form Lichenospliceria Lenormandi, Bornet, might 

 not at another time invade the latter ? Would it then fi'uetify in the 

 same way, show spores alike, &c. ? But the "parasite" which does 

 really invade the latter (as shown by this paper) is not the same. 

 Are these Scytonemicolous and Sirosiphonicolous parasites, then, so 

 extremely choice ? 



Again, two very closely allied forms of Scytonema now brought 

 forward likewise showed very distinct parasites, as evinced by their 

 spores, whilst those of one of them much resembled that of Sirosiphon 

 pulvinatus, an alga in itself sufiiciently unlike the other. 



In objection to the new theory, though it has much to say for 

 itself, in the meantime and whilst it is, as it were, on its trial, it might 

 be asked at what period of the life of the Scytonema or Sirosiphoti does 

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

 it make an entry ? It must be near the base, or at all events not 

 very high up, for the hypha is found growing pretty neai'ly ^;«r?.' 

 2)assu with the growth of a branch of the alga, and in the same general 

 direction. But why might not the hypha grow in the opposite direc- 

 tion ? Might it not sometimes enter near the apex and grow backward ? 

 Might we not sometimes expect to find hyphoe sticking out from 

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

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

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

 hypha appertaining to a particular plant have had its commencement 



