ANNOTATIONS AND ADDITIONS. 325 



istic form of the species of Erica, including Calluna (Erica) Vul- 

 garis, L., the common heather. 



"While, in Europe, Erica carnea, E. tetralix, E. cinerea, and 

 Calluna vulgaris, cover large tracts of ground from the plains of 

 Germany, France, and England to the extremity of Norway, South 

 Africa offers the most varied assemblage of species. Only one 

 species which is indigenous in the Southern Hemisphere at the 

 Cape of Grood Hope, Erica umbellata, is found in the Northern 

 Hemisphere, i. e. in the north of Africa, in Spain, and Portugal. 

 Erica vagans and E. arborea also belong to the two opposite coasts 

 of the Mediterranean : the first is found in North Africa, near 

 Marseilles, in Sicily, Dalmatia, and even in England; the second 

 in Spain, Italy, Istria, and in the Canaries." (Klotzsch on the 

 G-eographical Distribution of species of Erica with persistent corol- 

 las, MSS.) The common heather, Calluna vulgaris, is a social 

 plant covering large tracts from the mouth of the Scheldt to the 

 western declivity of the Ural. Beyond the Ural, oaks and heaths 

 cease together : both are entirely wanting in the whole of Northern 

 Asia, and throughout Siberia to the shores of the Pacific Ocean. 

 Grmelin (Flora Sibirica, t. iv. p. 129) and Pallas (Flora Kossica, 

 t. i. pars 2, p. 53) have expressed their astonishment at this disap- 

 pearance of the Calluna vulgaris a disappearance which, on the 

 eastern declivity of the Ural Mountains, is even more sudden and 

 decided than might be inferred from the expressions of the last- 

 named great naturalist. Pallas says merely : " Ultra Uralense jugum 

 sensim deficit, vix in Isetensibus campis rarissime apparet, et ulte- 

 riori Sibiriae plane deest." Chamisso, Adolph Erman, and Hein- 

 rich Kittlitz, have found Andromedas indeed in Kamtschatka, and 

 on the north-west coast of America, but no Calluna. The accurate 

 knowledge which we now possess of the mean temperature of several 

 parts of Northern Asia, as well as of the distribution of the annual 

 temperature into the different seasons of the year, affords no sort 

 of explanation of the cessation of heather to the east of the Ural 

 Mountains. Joseph Hooker, in a note to his Flora Antarctica, has 

 treated and contrasted with great sagacity and clearness two very 

 different phenomena which the distribution of plants presents to us : 

 on the one hand, " uniformity of surface accompanied by a similarity 

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