PERIODICAL LITERATURE 501 



scrub or grass-land is when artificial agencies are at work. Warming 

 goes so far as to say : "Were the human race to die out the grass- 

 lands of the lowlands of northern Europe would be changed back to 

 forest, their condition before the interference of man." 



In the paper by E. A. Woodruff-Peacock the writer contends 

 that woodland succession, including the natural degeneration of forest 

 to scrub or grass-land and the change from one species to another, 

 is primarily due to soil exhaustion. He states that species appear on 

 sites at definite historical periods. Thus in Lincolnshire, England, 

 Roman times brought in the beech and the Neolithic times the ash 

 and elm, as demonstrated by peat deposits. He states that during the 

 eighteenth century the great oak woods of north Lincolnshire dis- 

 appeared and its place was taken very largely by ash and elm. In 

 this case soil exhaustion is assigned as the cause of the passing of 

 one species and the coming in of another. 



The author states that when, in the progress of time, the seedlings 

 of a long predominant species fall just as they become wholly de- 

 pendent on the soil for their nourishment, it is an indication that they 

 are passing from that particular soil for at least a succession period. 

 It is emphasized that Lincolnshire was covered with oaks in the 

 seventeenth and early eighteenth centuries and that . there are still 

 left a few old standards, but no seedlings or young trees. When the 

 northern ancestors overran Lincolnshire in 400-1000 A. D. the beech 

 was already there in abundance. Since then the soil has had time to 

 become beech-sick, as exemplified in its decreasing distribution. He 

 observes that the reproduction among the old beeches that still survive 

 is not beech at all but ash and to a lesser extent, wych elm. The 

 author's conclusion from the study of historical evidence is soil 

 exhaustion for a given species is evidenced: 



(1) When the germinating seeds fail to survive on the soil. 



(2) When there are present in abundance self-sown, healthy 

 young trees of another species. 



(3) When a wood begins to show evidence of decline and a 

 gradual thinning of the stand, and when, before the end, it becomes 

 park-like unless other species come in to occupy the open places. 



(4) When the woodland for a time is taken by its peculiar under 

 species and scrub, although in its mid-vigor it easily maintains itself 

 against them. 



Regarding the latter it is noted that the under species only persist 



