454 THE ECOLOGY OF PLANTS. 



plants. Altogether the vegetation of this hollow indicates that it is 

 moist, and even marshy at times, but is never long under water. 



The ponds at Filey are thus instructive examples of aquatic and 

 marsh vegetation. The ponds themselves show every stage of transi- 

 tion from ponds of open water to marshy hollows, and even dry 

 hollows." 



422. Weeds of Cultivated Soil. The vegetation of 

 barren and economically useless lands moors, heaths, shores, 

 etc. has undergone but little change during all the centuries 

 that have passed since our country was first inhabited and 

 cultivated by man, though mountain vegetation has doubtless 

 been modified by grazing. Except in such localities as these, 

 the land has been largely disturbed by the operations of agri- 

 culture, forestry, drainage, etc. What has become of the 

 plants that once occupied what is now cultivated land ? They 

 have been driven from the fields, but with probably very few 

 exceptions they all grow now in the hedgerows, river-banks, 

 thickets, and wood-edges. 



There are many interesting points connected with the 

 weeds of cultivated soil. A garden or cultivated field is 

 usually surrounded by hedges, pastures, or woods, but its 

 weeds comprise few or none of the plants belonging to the 

 " natural " vegetation close at hand. The weeds have not come 

 from the neighbouring vegetation, and they could not in most 

 cases survive among the crowded hedgerow and meadow plants. 



This brings us to the next point that most of the weeds 

 of cultivated soil are annuals. Annual weeds depend almost 

 entirely upon man and his cultivation of the soil. They have 

 doubtless evolved from ancestors which, to escape competition 

 with perennials, grew on rocks, poor soil, sea-shores, etc., 

 and which, owing largely to their rapid growth and profuse 

 seed-production, invaded the fields tilled by primitive man, 

 and will now never leave until the cultivated ground is 

 allowed to return to its natural state. It is unnecessary to 

 point out how annual weeds can flourish, and be free from 

 competition with perennials, in cultivated fields bearing 

 annual crops such as wheat. The origin of many of these 

 annual weeds is very uncertain ; for instance, the common 

 Groundsel is never found wild, though the fleshiness of its 

 leaves suggests that its ancestor was a seaside plant (we 

 know this to be the case with several annual weeds). 



