250 



us. Trees of the lace-bark tribe and similar plants succeed ; we 

 wander for a time through a zone of evergreen forest trees. At a 

 height of 4,000 feet we lose the plants which had so far accompanied 

 us. A very small number of peculiar plants mark a quickly traversed 

 zone of deciduous trees, and we come among the resinous trunks of 

 the Canary pine. A zone of Conifers shields us from the sun's rays 

 up to a height of 6,000 feet, then the vegetation suddenly becomes 

 low, — from humble bushes it passes into a Flora which bears all the 

 characters of the Alpine plants, till finally the naked rock sets a limit 

 to all organic life, and no snow and ice bedeck the summit of the 

 mountains, only because its height of 12,236 feet does not, in a posi- 

 tion so near the tropics, extend up to the region of eternal snow." — 

 p. 246. 



Facts of this description inevitably lead to the conclusion that the 

 intensity of light, the pressure of the atmosphere, the constitution of 

 the soil, and conditions of temperature and moisture, all exercise con- 

 siderable influence upon vegetation. But this will not account for the 

 other class of facts adverted to ; it will not explain why the common 

 daisy {Bellis perennis) should occur in Europe (almost universally), 

 in Australia (where it has probably been introduced), in Northern 

 Asia, in some parts of Africa, and in South America, without deigning 

 to favour North America with its presence, except as a choice exotic, 

 tended with the most jealous care in botanic gardens. In the words 

 of our author, it does iudeed seem to us 



" Wholly the result of caprice, that particular plants are distributed 

 widely over the globe, while others must live cribbed in the narrowest 

 spot, as, for instance, the Wulfenia, occun*ing exclusively on the Ca- 

 rinthian Alps ; that particular families, like the Coinpositse, flourish 

 abroad over the whole earth, while others, like the peppers and the 

 palms, only occur between very definite degrees of latitude on either 

 side of the equator, the Proteacese only in the southern hemisphere, 

 the Cactus tribe only in the western half of the earth. Just as inex- 

 plicable is the mode of distribution of the families of plants. While 

 the palms diminish in number from the equator into high latitudes, 

 the Composite attain their highest development in the zones of mean 

 temperature, their number of species diminishes from these in both 

 directions, equally towards the equator and towards the poles ; while, 

 finally, the grasses increase constantly from the equator towards the 

 poles."— p. 257. 



Such considerations teach us the absolute necessity for the further 

 accumulation of facts ; and the necessity is not limited to this parti- 



