RECENT RESEARCHES INTO THE NATURE OF LICHENS. 157 



contour which characterises the gonidia of the thallus of the 

 Lichen in question. 



The conclusions arrived at as the result of the foregoing inves- 

 tigations areas follows: — (1) in those Lichens which possess 

 hymenial gonidia the thallus is regularly produced by the coming 

 together of the spore of the ascomycetous Fungus and the Alga ; 



(2) the hymenial gonidia when actively dividing derive their 

 nutriment from the constituents of the structure in which they 

 are enclosed : in view of the small quantity of chlorophyll 

 which they contain, it does not seem probable that they give up 

 to the Ascomycete any of the products of their assimilation ; 



(3) if it be suggested that the hymenial gonidia appear to resem- 

 ble the entophytic algal colonies found in Anthoceros, AzoUa, 

 Gunnera and others, it must be remembered that they are of 

 extreme physiological importance in the economy of the Lichen 

 in that they afford to the germinating spores material for the 

 formation of a new thallus. 



With this account of StahFs observations this resume of the 

 lichen-gonidia discussion must for the present close. It is quite 

 evident that the theory of the structure of Lichens which was 

 suggested originally by De Bary and first tested experimentally 

 by Schwendener is gradually becoming established upon a sure 

 foundation of accurate observations. It will be noticed that the 

 objections brought against it are, on the whole, more of a theo- 

 retical than of a practical nature. The theoretical objections 

 may be regarded as silenced by the researches above alluded to 

 of Winter, Frank and Stahl, and if further experimental evidence 

 be required it is to be found in StahPs paper on the sexual repro- 

 duction of the CoUemacese, which will be discussed hereafter. 

 The practical objections are mainly the observations of Arcangeli 

 and of Minks, which seem to shew that gonidia may be deve- 

 loped from hyphse. It must be remarked that although these 

 observations tend to prove the same fact, yet they differ widely, 

 and therefore cannot be regarded as being confirmatory the one 

 of the other. It remains to be seen whether or not other ob- 

 servers will in the future be successful in repeating these observa- 

 tions, and if they will endorse the interpretations which have been 

 put upon them. 



Vol. iviii.— new seh. 



