RECENT OBSERVATIONS ON THE GONIDIA QUESTION. 123 



fall not just upon but close to the iVb*^oc-colonies ; the ger- 

 minating filaments in this case may partly penetrate into the 

 Nostoc and partly into the substratum, and all the con- 

 ditions for the production of Collema would be complete. With 

 much more minute algse, which are the gonidia-formers of 

 heteromerous lichens, these may in any case originate by later 

 importation of spores, because even if the spore falls ju.st 

 upon the alga, it is possible that the germinating filaments 

 may still reach the substratum, since they mostly far exceed 

 in length the diameter of the algse. 



2. The explanation given by Miiller of the relation be- 

 tween Nostoc and Collema, founded on Reess's experiments, 

 — that we have to do with a peculiar kind of alternation 

 of generations, — is nothing else than the last desperate effort 

 to hold by the organic individuality of the homoiomerous 

 lichens by means of a mere fight about words. The expres- 

 sion ^alternation of generations' (generatiewisseling), taken 

 in its widest sense, is applied to the phenomenon of an 

 organic individual in reproduction producing first a form 

 wholly different from that which brings it forth, and only the 

 direct or indirect progeny of this generation becoming like the 

 first. Thus, to regard Nostoc as an ' alternation ' ot Collema 

 it should alone be able to furnish Collema ; this, in reality, is 

 not the case, so that, without completely overstraining the 

 expression ' alternation of generations,' it cannot be applied 

 to the relation betAveen Nostoc and Collema. It is clear, 

 however, that Miiller merely wants to replace the ^^orc? para- 

 sitism by the phrase ' a special kind of partial alternation of 

 generation' when he says, if the increase of perfect indivi- 

 duals of Collema takes place by spores, some gonidia must 

 be already present, which then, in combination with the 

 intruding hyphse, furnish the perfect apothecia-bearing indi- 

 viduals. No competent judge will, I think, controvert that, 

 following Miiller's own description, we have here to do with 

 parasitism in the strictest sense of the word." 



The following reproduces the principal portions of the 

 second section of Treub's memoir, recording his original 

 researches : — 



Relations between Gonidia and Hypha. — Although, in the 

 course of the present summer, the copious treatise of Bornet 

 has appeared, in which the relation between the gonidia and 

 hyphse is discussed in a decisive manner, I still feel myself 

 compelled briefly to communicate my own long-continued 

 researches on the above point. * * * * 



It is well known that it is upon Bayrhoffer and Speer- 

 schneider's authority that the origin of the gonidia from the 



