244 ORALLY. 



shores and banks of the rivers which are perpetually humid, 

 produce a vegetation too exuberant for any birds to find 

 their food among its roots. In those climes of the excess of 

 solar action, the growth of the single year on the marshy 

 bank the bamboo, and even the grass, rivals our groves in 

 altitude j and the mangroves by the margin of the sea sur- 

 pass our forests in loftiness of growth, and entanglement of 

 branches. Therefore it is only at the middle temperature 

 between those extremes that such birds as the crakes could 

 find a permanent dwelling ; and then, as water is an essential 

 element in the adaptation of the place to them, the line of 

 those haunts which approach the most nearly to being per- 

 mananently suitable to them, varies more in curves and zig- 

 zags northward or southward, than even the isothermal lines, 

 or lines of equal temperature, irregular and hard to be deter- 

 mined as these are. 



Thus it may with truth be said, that the crakes, like the 

 warblers, have no permanent abode upon the globe ; but that 

 they must have their declinations northward and southward 

 with that sun, the variations of whose influence call forth 

 their cover and their food at different periods in different 

 latitudes. But though, in consequence of that very simple, 

 and therefore exquisitely beautiful, motion of the earth, 

 which produces the seasons, the summer may be (and is) as 

 hot in Lapland as under the equator, the season and the 

 vegetation are not the same. The equatorial plant feels no 

 winter ; has never to overcome to inertia of a temporary 

 death ; and thus it grows apace till one leaf would cover a 

 tent, and one tree overshadow an acre. In the extreme 

 north, again, half the action of the summer sun is expended 

 in calling forth the annual vegetation from the temporary 

 death of the winter. 



Thus the migration of such birds as the crakes is confined 

 both northerly and southerly; and as they have different 



