116 W. ARCHER, 



from the hypha-branches ; hence, for the Omphalarieee or for 

 the Gloeolichenes (Fries), he holds the new theory to be im- 

 possible. He would be inclined to assume for the remainder 

 of the cla«s that — at least as regards the primordial gonidium 

 of the gonidia-colonies — there must have existed a genetic 

 connection between it, the gonidia, and the hypha, but that 

 it may be probable that this formation of gonidia from the 

 hypha-branches may take place only in the very young con- 

 dition of the thallus, and that subsequently the gonidia 

 increase merely by subdivision. 



As regards CoUemea, indeed, and the experiments insti- 

 tuted by E,eess^ in causing its spores to germinate on Nostoc, 

 and develope in the substance of the latter a richly-ramified 

 mycelium, and thus (as Reess and Schwendener hold) convert 

 the Nostoc into Collema, Miiller, whilst accepting the facts, 

 has another interpretation to propound. This he sums up 

 in the following terms : — 



1. Collema is dimorphic, and it has (L) a perfect state in 

 which it possesses hyphae and fructifies, and (2) a secondary 

 state (known as Nostoc) which never bears either hyphse or 

 apothecia. 



2. The secondary (not, perhaps, merely younger) Nostoc- 

 state of Collema reaches the perfect state only through the 

 penetration into it of the hyphse belonging to its perfect 

 condition, which are derived from a spore or simply from 

 "root-hairs," and through a "vegetative copulation^' (so to 

 say) of the hyphse with the gonidia. 



3. Collema in perfect (hypha- and apothecia-bearing) 

 individuals propagates itself mostly by soredia. 



4. An increase of perfect individuals is also possible by 

 spore-germination, but a secondary development of simple 

 gonidia {Nostoc) must precede it ; the former then acquires 

 the faculty of producing apothecia by means of the spore- 

 filaments or root-hairs (of Collema) penetrating into the 

 latter. 



5. Simple spore-germination without the co-operation 

 of the secondary state (Nostoc) produces no thallus (gonidia 

 and hyphae), and, on the other hand, simple gonidial- 

 iVbs^oc-formation, without the co-operation of the perfect 

 state (spore filaments or root hairs), .remanis destitute of 

 apothecia. 



Thus, Dr. Miiller would take Collema for the complete 

 state, Nostoc for the secondary state of this dimorphic plant, 



' Reess : " Ueber die EntsteliuDg der Plecbte Collema glaucescens 

 Hfmm. etc.," in 'Monatsbericbf d. k. Akad. d. Wiss. zu Berlin,' Oct., 

 1871, p. 523. 



