528 ON MURAL OR WALL PLANTS. [AuffUSt, 



number is expected to increase. The veterans in science, who 

 honour the journal with their notice, will excuse it, as it is 

 meant to help their juniors to fill up the gaps which time and 

 casualty make in our ranks. Habitat is from habito, "I dwell," 

 and is employed by botanists to signify the sort or kind of 

 locality where the plant usually grows, the soil, exposure, shade, 

 moisture, dryness, or any other quality of the place. The terms 

 station or locality denote the precise place where a species is to 

 be found, and the latter term is used in preference to the for- 

 mer, which is now popularly applied to railway stations. For 

 example, the habitat of Hottonia palustris is aquatic, because it 

 grows in water or in watery places : this is general ; whatever 

 the specific locality be, the plant is found only in water. Lo- 

 cality is special : it indicates the precise place or places where 

 the said plant grows ; not in every place where there is water, 

 but only in some particular places, as Streatham Common, 

 near Tooting ; Letchmere ditches, in Battersea-fields ; near 

 Woking town, on the road to Clandon, etc. 



It is not intended to give a complete list of mural British 

 plants, but to notice some of them in a cursory way. Another 

 preliminary remark is necessary, viz. that few or any plants 

 (phsenogamous plants only are to be understood, though pro- 

 bably other plants are in the same category) are exclusively 

 confined to walls, or to walls and roofs, or to walls, roofs, and 

 ruins. Most of them are to be found in other places, and some of 

 them in several very dissimilar habitats. Many Grasses are mural, 

 but none of our British Grasses are exclusively so. Poa annua, 

 P. pratensis, P. compressa, etc., are found on old walls, though 

 they grow also on the ground. Several Festucas and Brome 

 Grasses select walls even in preference to soil. Carices (Sedges) 

 do not grow on walls. From this it may be inferred, that fibrous- 

 rooted plants, which the Grasses are, find on walls a habitat 

 adapted to their economy, and also that thick or fleshy-rooted, 

 or creeping-rooted plants, as the Carices are, do not find on 

 walls a habitat suited to their necessities. There are apparent 

 exceptions to this law. Echium vulgare abounds in light sandy 

 fields, where it shuns walls. In better soil, it prefers a mural 

 situation, where it thrives equally well. Cerastium triviale grows 

 on walls, on dry exposed banks, by roadsides, in pastures, and 

 in boggy places, among rank vegetation, where it is very luxu- 



