224 Limuean Society. . 



those species the introduction of which may be traced to artificial 

 causes, regarding those alone as indigenous which are coeval with the 

 soil. Agriculture, Medicine, and even Religion, have each swelled 

 our list. Coronopus didyma is not found in England but at ports, 

 and seems to be a particularly migratory species. It may be found, 

 he says, in almost every latitude where ships frequent j — at Lisbon, 

 Madeira, Rio Janeiro, the Cape, Sydney. He thinks the same dis- 

 position may be witnessed in many of the Cruciferae, and adduces as 

 instances, Sisymbrium Irio, and Thlaspi campestre. Whether the cause 

 of such phenomena is to be sought for in the structure of the seed, 

 or in the pabulum necessary to the growth of the plant, remains to 

 be determined. The Blatta orientalis (common Cock-roach), and 

 the Norway Rat, which has eaten up the old Black Rat, are instances 

 from the animal world, showing a similar tendency. 



In order to ascertain whether a species be indigenous, it is of im- 

 portance to ascertain upon what stratum, or in what places, it ter- 

 minates its range. Many southern plants he finds terminate their 

 northern range upon old walls, such as Sisymbrium Irio and tenuifo- 

 lium, Dianthus Caryophyllus, Teucrium Chamccdrys, &c. Others 

 again abounding in the south, finish their course by attaching them- 

 selves to some of the warmer strata, as to mountain limestone, or 

 new red sand-stone. Hutchinsia petrcea grows in the Olive country 

 so abundantly that it is gathered as a salad. With us it finds only 

 a few localities, and those always on mountain limestone. Campa- 

 nula patuta finds its most northern accommodation in England on 

 the new red sand-stone. It has one other station with us on chalk, 

 which is its place in Brittany. 



The sea-coast also carries many plants further north, than inland 

 situations can do. The Common Privet for instance, though so abun- 

 dant in the south on the chalk and gravels, becomes rarer as we 

 proceed to the north. In Scotland it affects the coast, and in Sweden 

 is wholly confined to it. On the other hand, plants which belong to 

 a more northern latitude and to more primitive countries, do not 

 terminate their southern range on our warmer and richer soils. The 

 author suspects Daphne Mezereum not to be English, because it is 

 found only on the more recent strata. 



The stratum producing the greatest number of rare plants with us 

 is the mountain limestone ; and although but a small portion of this 

 rock should appear above the surface surrounded by other rocks of a 

 different structure, it seems to have caught the rarer species. The 

 district of Gower, Brean Down, St. Vincent's Rocks, Orme's Head* 

 are examples. 



Next to mountain limestone the Bury sand seems to be a fa- 

 vourite station of unusual productions. Veronica triphyllos and verna, 

 Vicia lathyroides, Tillcea muscosa, Scleranthus perennis, &c. &c. grow 

 there. 



The richest soils are the least productive of rare species. Slaty 

 countries, excepting the highest elevations, are also singularly de- 

 ficient. 



Many of our promontories are remarkable for the rarities they pro- 

 duce 



