322 HOW SEEDS ARE SO WN. 



the globe, while others are confined within narrow limits. 

 Some of the common weeds in Britain, such as chickweed, 

 shepherd's purse, and groundsel, are found at the southern ex- 

 tremity of South America. Laura minor and trisu/ca, Convol- 

 vulus septum, Phragmites communis, Cedium Mariscus, Scirpus 

 lacustris, Juncus effusus, and Solatium nigrum, are said to be 

 common to Great Britain and New Holland. Nasturtium 

 officinal e, and Samolus Valerandi are very extensively diffused, 

 and they may be reckoned true cosmopolites. They are both 

 natives of Europe, and they occur, the former near Rio Janeiro, 

 the latter at St Vincent. The lower the degree of development, 

 the greater seems to be the range. Some cryptogamic plants, as 

 Lecanora subfusca, are found all over the globe. 



" Man has been instrumental in widely distributing culinary 

 vegetables, such as the potato, and the cereal grains, as well as 

 many other plants useful for food and manufacture. Corn 

 plants, such as barley, oats, rye, wheat, spelt, rice, maize, and 

 millet, are so generally cultivated over the globe, that almost 

 all trace is lost of their native country. They can arrive at 

 perfection in a great variety of circumstances, and they have 

 thus probably a wider geographical range than any other kind 

 of plants. 



" As regards these plants, the globe may be divided into fve 

 grand regions the region of rice, which may be said to support 

 the greatest number of the human race ; the region of maize; 

 of wheat ; of rye ; and lastly, of barley and oats. The first 

 three are the most extensive, and maize has the greatest range 

 of temperature. 



