VIII. LATITUDE. 457 



separation between the floras of Mid and North Britain, 

 as well as to the line between those of England and Scot- 

 land ; certain species which are found under distrusted 

 conditions in the latter division, being reckoned in the 

 list for the former division only, and not admitted among 

 the native plants northward of the estuaries of Clj'de and 

 Forth. 



In accordance with the northerly decrease in the total 

 flora, most of the orders exhibit a decreasing number of 

 species in the same direction, when the ternary figures in 

 the middle column of the * distributive census' are compared 

 together. The rate of numerical decrease northwards is 

 very unequal among the orders. Thus, Composit<e ap- 

 pear to decrease by very few species in proportion to 

 their total numbers ; being only one-eighteenth of the 

 whole, or 6 out of 108, the north compared with the 

 south. The absence from North Britain of various 

 English species of that order, is compensated there by 

 the accession of many alleged species of Hieraciuvi, and 

 some species of other genera among the alpine or arctic 

 plants. On the contrary, Umbelliferce decrease more 

 decidedly, Chenopodiacece and Eiiphorhiacece still more 

 decidedly, from south to north. 



In the list referred to, llosacece and LcguminifereB ap- 

 pear on equality by actual numbers in North Britain ; 

 but in South Britain the former order is one-seventh more 

 numerous, chiefly through the genus Ruhus, the segregate 

 species of which have not been so much recorded for 

 North Britain ; where, indeed, several of them may likely 

 be quite absent. FiUces and OrchidaceoB are numerically 

 equal in South Britain ; becoming less equal in Mid 

 Britain, and very unequal in North Britain. Lycopo- 

 dlacete and Plantag'macede show even numbers in all tliree 



VOL. IV. S N 



