156 STATES OF THE EIVER PLATE. 



of them utterly devoid of green herbage during the heats 

 of summer and early autumn, more especially in a season 

 of less than the average rainfall. On the other hand, the 

 lower lands, thinner in vegetable mould, and more clayey, 

 are under water after heavy rains, and wet and puddly 

 after every medium rainfall, and at such times the vege- 

 tation is by consequence deficient in alkalies and saccha- 

 rine matter, poor in nutriment constituents, and tending 

 to scour ; but when the rainfall is scant and insufficient 

 for the higher grounds, more especially during early 

 summer, these low lands are clothed with nutritious and 

 palatable herbage and sweet grasses, in many instances 

 intermingled with two or three varieties of the melilot. 



The most remarkable peculiarity of the medium and 

 higher lands is the full possession taken of immense tracts 

 at certain seasons by the variegated thistle, which over- 

 shadowing every other herbage, chokes it and causes 

 almost every vestige of it to disappear. Other tracts are 

 held possession of by the hard perennial thistle (wild 

 artichoke) intermingled with the plants, which in the 

 lower stages of its growth is the very best of grasses, but 

 in the months of its maximum growth it covers the ground 

 completely, bidding defiance to the entry of almost any 

 animal into its prickly domain. 



With few exceptions, the grasses, clovers, and various 

 kinds of palatable herbage are annuals, and these consti- 

 tute two distinct series, growing and seeding in different 

 seasons of the year, and making no sign whatever at other 

 periods. 



One series of these grasses does not make its appearance 

 until after the heats of the summer, and the first autumn 

 showers cause them to spring into life. They develop, 

 seed, die down, and disappear with the autumn, and are 

 succeeded by the other series, comprising both grasses and 



