XXII. 



XOTE ON THE SCHWENDEXERIAX THEORY OF LICHEXS. 



By E. B. Ckoft, R.N., F.L.S., F.R.M.S., Hon. Sec. 



Read at Hertford; 2bth January, 1881. 



I CANNOT better describe the theory as to the nature of lichens 

 which is variously styled "The Algo-Lichen Hypothesis," the 

 "Dual-Lichen Hypothesis," and the Schwendenerian Theory of 

 Lichens, than by quoting the commencement of a paper by the 

 Rev. W. A. Leighton in 'Grevillea' (vol. ii, p. 122), in which 

 periodical will also be found the arguments for and against the said 

 theory. 



Mr. Leighton says : " Much attention has been of late devoted, 

 and is still devoted to the subject of the gonidia of lichens. Two 

 theories or opinions have sprung from these researches, which are 

 respectively supported by great and learned savans. Those whose 

 studies are chiefly physiological maintain that the filamentous 

 tissue of the thallus of lichens is a fungus which grows para- 

 sitically on an alga, which it envelopes and carries on with it in 

 its growth so as to constitute the gonidia. On the other hand, 

 true lichenologists, whilst admitting the apparent similarity of 

 gonidia to certain algae, do not consider them as such, but as 

 special organs of multiplication or propagation of lichens." 



Although Professor Schn^endener propounded this theory in 1869, 

 and although many experiments have been made by various ob- 

 servers to test its truth, opinion still is divided. Sachs, in his 

 ' Text-Book of Botany ' (p. 262), says : " There can no longer be 

 any doubt that the lichens are true fungi of the section Ascomy- 

 cetes, but distinguished by a singular parasitism. Their hosts are 

 algae which grow normally in damp places but not in water." As 

 many introductory works on botany are founded on Sachs' work, 

 this is repeated, learnt, and believed by many ; while on the other 

 hand Dr. ISTylander, admittedly the gxeatest Lichenologist of the 

 age, terms the hypothesis "absurd," and Dr. M. C. Cooke classes 

 together the advocates of the theories of Table-turning, Tichborne, 

 and Schwendener. 



About two years ago I made my first attempt to build a lichen, 

 or rather I found in a small phial that which advocates of the 

 Schwendenerian theory would have no doubt claimed as such ; and 

 as I have just repeated the experiment with the same result, I will 

 briefly describe the modus operandi, in the hope that other members 

 may by their observations throw further light on the subject. 



I placed a gathering of Protococcus pluvialis^' in a small phial in 



* In both cases the Protococcus was from a cast-iron shell at the base of a 

 fountain in the garden of Mr. C. W. Nuun, of Hertford. Mr. Nunn has had 

 tliis Protococcus under observation for several years, and considers it to be a 

 distinct red variety. 



