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growth ; but the different nature of the soil has also great influence 

 on their growth. The mass of well-decomposed earth, the presence 

 of boulders or firm rock, the exposure of the locality, the humidity of 

 the soil, and in some degree also its inclination, have so great an 

 influence on the growth of the tree, and are moreover especially in 

 the lower regions so irregularly distributed, that the influence of ele- 

 vation, which should be most closely connected with the changes of 

 chmate, may be and is partially obliterated. Very frequently indeed 

 in investigations of the geography of plants, a similar concurrence and 

 a mutual correlation of the various causes by which the changes of 

 vegetation are produced, are to be recognized. The observation of 

 the progress from year to year shows that very frequently considerable 

 variations occur in the amount of growth in separate stems. These 

 are not, however, connected with definite years of the development, 

 but irregularly distributed during the life of a tree. As they com- 

 monly extend over a long series of years, and do not agree in different 

 trees for definite numbers of years, they cannot be produced by the 

 climatic circumstances of unfavourable years. The larger oscillations 

 of growth are dependent, on the contrary, on the nature of the soil, 

 inasmuch as the roots during their extension meeting with moi'e or 

 less favourable and rocky spots, the productiveness of a tree may be 

 essentially changed during many years. 



An enumeration of all the phanerogamous plants found in the Up- 

 per Moll district (in the Tauern, in Upper Carinthia) at between 7000 

 to 8000 Paris feet high, and between 8500 to, 10,000 feet, gave for the 

 former region, the subnival, 224 species, for the latter, the nival, 32 ; 

 while Prof. O. Heer obtained from the same regions in Glarus, in 

 Switzerland, 219 and 12. Many families, as for example Boragineae, 

 Euphoi'biaceae, Geraniaceae, Labiatge, Liliacese, Stellatae, Umbelliferae, 

 &c., compared with the lower regions and with Germany, diminish evi- 

 dently and sometimes very strikingly in species in relation to the sum of 

 Phanerogamoe. In some others no such regular differences are found 

 in relation to height. A remarkable relative increase of species in 

 connexion with increased elevation, is found in Saxifrageae and Primu- 

 laceae ; and may also be remarked in Carapanulaceae, Caryophylleae, 

 Compositai, Gentianeae, and others. This depends, not on an abso- 

 lute increase of species of these families, but on a diminution of the 

 species of the other ftimilies. Monocotyledones generally diminish 

 with height in relation to Dicotyledones ; except that in the nival 

 region and in the highest localities this proportion appears to be 

 somewhat undefined. The covering of snow also is not completely 



