106 sorby's researches on chromatology. 



various facts described above, the following arrangement expresses 

 every thing so far known respecting the distribution of the different 

 colouring-matters : — 



Actinia. 



Anthea cereus, var. smaragdina. 



Olive group of A Igce. 



Red Algoe. Oscillatorice 



Porphyra. Peltigera. 



Green Algoe. Lichens. 



Higher Cryptogamia. 



Highest classes of plants. 



The colouring -matters found in Actinia? are very various, and 

 it is only particular species that contain those found in Alga?. 

 Lichens, as a whole, are characterized by a number of what may be 

 called accidental constituents— such, at least, as occur in one species 

 and not in another closely allied to it. Many of these are almost 

 or quite colourless substances, which easily give rise to colouring- 

 matters when treated with various reagents. This fact, combined 

 with their partial distribution, is taken advantage of in studying 

 lichens as a means for distinguishing closely connected species. 

 Their more constant and aj)parently fundamental colouring-matters 

 correspond with those found in the higher classes of plants, but 

 differ considerably in relative proportion, the lichnoxanthines usually 

 being relatively more abundant. 



ON SOLORINA BISPORA. 

 By Dr. J. Stirton. 



By way of reply to Mr. Crombie's note on Solorina bispora (Nylj, 

 perhaps I may be permitted to state the considerations which have 

 weighed and still weigh with me towards the retaining of it as a 

 species. 



Since detecting this lichen for the first time in 1871, on Ben 

 Lawers, I have secured it on almost every mountain in Scotland 

 that I have climbed of a greater elevation than 3000 feet. Accord- 

 ingly, so far as my experience goes, it is more frequent than S. 

 saccata, which is usually found, besides, at much lower elevations 

 — a fact which, in my estimation, ought not to be wholly ignored 

 in the question of specific distinction. In all these instances (four 

 in number) the thecae are 2-spored, without exception. Occasion- 

 ally, it is true, a one spored theca may be seen, where the spore 

 is larger than usual, viz., as in one specimen (*1 X "054 m.m.), but, 

 as is well known, especially in the larger spored lichens, such a state 

 is easily accounted for physiologically, although the converse does 

 not hold true. 



