
‘ CITIZENSHIP OF PLANTS. 397 
as Heath, Sedges (Carices), Rushes, and many Grasses. Some 
of the last-mentioned family, are certainly introductions. Few 
Carices, it is to be presumed, are so, because they are worthless 
as economical plants, but some of them have probably been in- 
troduced. How many of the trees in our parks, woods, hedges, 
and homesteads, to omit orchards and shrubberies, are of British 
origin? The half of them? Probably not. Nine-tenths of our 
annual weeds depend on an artificial condition of the soil, and 
cannot, in strict consistency, be deemed natives while botanists 
exclude plants that grow only on artificial erections, such as 
walls, roofs, ruins, or in hedges, woods, etc., for these annuals 
are dependent on an artificial condition of the soil. 
Holosteum umbellatum and Saxifraga tridactylites are in- 
structive examples of the distribution of plants, assuming that 
their Continental habitats are correctly given, and if it be univer- 
smemtnorce 
x 
sally true, as we believe it is, that they are confined to roofs and 
walls in England. In the Continent the usual places of growth » > "~ ist » 
of Holosteum umbellatum are fields, waysides, and walls, etc. ; 
warm declivities (sonnige Abhidnge) and rocks produce Sami- 
fraga tridactylites. The plants are both self-propagated, but 
they grow on artificial erections or in ground in an artificial 
state. If they originally grew on the ground in England as 
they do on the Continent, how comes it to pass that they are 
now found chiefly, if not exclusively, on walls and roofs? Se- 
dum album, 8. dasyphyllum, 8. reflecum, and Sempervivum tec- 
forum grow commonly, even in the Continent, on roofs and 
walls. In Southern Germany S. dasyphyllum grows on rocks. 
On the Continent rocks are stated to produce Sempervivum tec- 
forum, but by the habitats, walls and roofs beimg placed before 
rocks, it may be presumed that the usual habitats are the for- 
mer. Can it be said that all these plants would not grow on 
rocks in England, if anybody thought it worth while to plant 
them there? We know that they are planted on walls where 
they live and increase. 
The Houseleek is common in Gothland, teste Linneo, and 
its localities, of which he reports many in his journey through 
that island, are invariably such as they are here, walls and roofs. 

It is also far more common in Scotland than in the south of - 
England ; and we have seen that it grows on rocks in Germany, 
though roofs and walls seem to be its choice. In Gothland it is 
