24 ANDREjEACE^. 



The species of Andreaea inhabit silicious and quartzose (not 

 calcareous) rocks, in alpine and subalpine regions of both 

 hemispheres, chiefly in the higher latitudes. In Europe it is in 

 Scandinavia that they are found in greatest abundance and variety, 

 and there are several endemic species there. 



It will be found a material aid in the determination of these 

 plants to soak the leaves, or heat them for a minute or two over 

 a spirit lamp, in strong caustic soda or potash ; this renders them 

 more transparent and elucidates the structure of the cells and 

 nerve. Care must be taken, in examining the leaf margin, to 

 avoid taking for a normal condition the eroded appearance of the 

 cells which, in older leaves especially, is often found to obtain, 

 from the wearing away of part of the cell wall ; this often gives 

 a false appearance of papillosity, crenulation, or dentation, or it 

 may suggest a more or less hyaline border to the leaf, and in the 

 nerved species may easily lead to an erroneous conclusion that the 

 nerve is excurrent. 



2. ANDRE^3A Ehrh. 

 The only genus. 



j / Ls. nerveless 2 



\ Ls. singly nerved 3 



2 /Ls. ovate-lanceolate, papillose, obtuse or more or less acute 1. fetrophila 



\Ls. obovate-spathulate, shortly acuminate, smooth 2. alfina 



/Ls. all similar, papillose, nerve narrow 4. nivalis 



\Stem ls. smaller than perich. Is., smooth or nearly so 4 



/ Nerve thick, occupying nearly all upper part of subula .3*. crassinervia 



\Nerve less defined, occupying only middle % of subula. .3. Rothii 



A. Eu-Andre^;a. 



Perichaetial bracts different from the leaves, erect and con- 

 volute, nerveless, or almost so. Capsule 4-valved. 



1. Andresea petrophila Ehrh. (Tab. VIII. D.) 



Tufts small, olivaceous or dark brown. Stems slender, |-i 

 inch high, simple, or several times forked, usually erect. Leaves 

 crowded, imbricated or more or less turned to one side, small, 

 ovate- or oblong-lanceolate, usually patent from an erect base, often 

 falcato-secund, narrowed at apex but usually obtuse, sometimes 

 with a minute apiculus formed of a single cell, sometimes more 

 acute, the tip often oblique ; margins incurved, entire ; nerveless, 



