REV. J. M. CROMBIE OX THE ALGO-LICHEX HYPOTHESIS. 263 



the gonidia of Physcia parietina. Similarly he reviews Sehwen- 

 dener's other group, the Phycochromaceje, and finds the following 

 genera belonging to it furnishing gonidia to various genera and 

 species of Lichens :— (1) Calothrix,Ag.,to Lichina, Ag.; (2) Scyto- 

 nema, Ag., to Ephebella Hegetscliveileri, Itz., to the cephalodia of 

 Stereocaulon ramulosum, Sw., and to various Pannarive; (3) 

 Lyngbya, Ag., to Stereocaulon ramulosum, Sw. ; (4) Nostoc, Vauch., 

 to Collema, Arnoldia, Physma, Leptogium, Obryzum, the cepha- 

 lodia of some Stereocaula, Nephromium, Stictlna, and certain 

 Pannarice ; (5) Stigonema, Ag., to Lichenosplucria Lenormandi, 

 Born., Spilonema paradoxum, Born., Ephebe pubescens (L.), and 

 the cephalodia of Stereocaulon furcatum, Fr. ; (6) Glceocapsa, 

 Kiitz., to Synalissa, Omphalaria, Phylliscum (as formerly shown 

 by Schwendener), Cora, and certain cephalodia of Stereocaulon. 



Of these Algal s, as observed by Bornet, a small number of 

 species furnish the gonidia for a great many different species 

 and even genera of Lichens. As to the relation between these 

 and the hypba>, he affirms that there is not the least evidence 

 that the gonidia originate from the hyphae any more than the 

 hyphae from the gonidia ; but that, on the contrary, the two are 

 originally quite independent, and that their union is a subsequent 

 event. This union, he acknowledges, is difficult to be seen in the 

 higher Lichens ; but in several of those enumerated above, and 

 reviewed by him, he has been able to detect the manner of ad- 

 hesion. For, while in the great majority of Lichens the hyphae 

 envelop the Algals and form a more or less embracing network 

 around them, yet in some instances, according to his observations, 

 the union is something more than mere contact, being a pene- 

 trating by the hyphae into the interior of the algal-cells. In 

 such instances of penetration, e.g. in Arnoldia minutula, Born., 

 the cell, he says, becomes enlarged, the wall thickens, the con- 

 tents become colourless ; at length the wall shrivels up, and the 

 gonidium finally becomes a dead membrane. Various other 

 minor points as to the relation between the hyphae and the 

 gonidia are touched upon by Bornet, which it is not necessary to 

 enter upon for our present purpose. Suffice it to say that, as the 

 general result of his investigations, he concludes that he is 

 fully warranted in laying down the two following propositions. 

 1. Every gonidium of a lichen may be referred to a species of 

 algal. 2. The connexion of the hyphae with the gonidia is of 

 such a nature as to exclude all possibility of the one organ being 



