THE INFLUENCE OF MAN. 331 



the grass tufts, spaces are left, which are at once 

 covered by the protonema of these mosses and by 

 liverworts. When the ground becomes a degree more 

 saturated, Eushes, or perhaps Aira caespitosa, will 

 develop, and marsh-loving weeds, such as the Spearwort, 

 Senecio aquaticus, and Caruni verticillatum, will replace 

 Senecio jacobaea, Ranunculus acris, and Heracleum 



spondylium. 



On the other hand, in good soil, where there is no 

 tendency to becoming waterlogged, and especially if 

 the grass is not properly watched, tall herbaceous 

 weeds, such as the Thistles, Ragwort, Cow Parsnip, etc., 

 will soon appear, and almost cover the field. These, as 

 shown in a previous chapter, are preparing the way for 

 the natural forest. 



Thus, grasslands are decidedly artificial productions, 

 and this is, of course, also the case with arable lands. 

 The crops grown in this country are all, with one or 

 two exceptions, foreign plants. Of wheat, the original 

 form is unknown. An allied species is found from 

 Achaia to the Caucasus and Mesopotamia. This form 

 Triticum monococcum has been discovered in the Lake 

 Dwellings of the Stone Age in Switzerland ; and it has 

 also been discovered at Troy. Cultivated varieties of 

 the ordinary wheat ( Triticum sativum) also occur in the 

 Lake Dwellings ; and grains of a form closely allied to 

 the ordinary wheat of to-day have been found in 

 Egyptian graves. Oats may have originated from the 

 Wild-oat {Avena fatua\ which is not uncommon in 

 Britain, or from similar species. This may have been 

 a native of Southern Europe or Western Asia. The 

 original form of the Rye plant {Secale montanum) 

 occurs in Spain, Greece, Armenia, and as far east as 

 Central Asia, and was probably first cultivated in 



