570 JOUKNAL OF THE KOYAL HOETICULTUKAL SOCIETY. 



Vegetation Affected by Agriculture in Central America. By 



A. F. Cook (U.S.A. Dep. Agr., Bur. PI. Ind., Bull. 145; 1909; plates). 



Much has been said about the influence of environment on primitive 



man. This pamphlet is intended to show how profound and lasting has 

 been the influence of primitive man on his environment. Various facts 

 support the conclusion that the Central American region was once one 

 continuous forest, and yet it may be doubted now whether any truly 

 virgin forest still exists there. Everywhere even in the densest tropical 

 growth you may come upon the ruins and relics of extinct civilizations, 

 civilizations which disappeared not through political changes or sudden 

 catastrophes, but because primitive methods of agriculture reduced great 

 tracts of land inhabited by peoples who lived by agriculture into the 

 condition of deserts, in which agriculture was impossible. Some of these 

 remains point to successive cultivation of the same regions in widely 

 separated ages, and the stages of the long struggle between man and 

 nature may be traced through existing conditions brought about by the 

 methods of Central American Indians to-day. 



Forest land is cleared by burning and grubbing, or even by burning 

 alone ; corn is planted, and the encroaching grass kept in check by 

 further burning, until the surrounding forest is driven away far beyond 

 the limits of the township. Gradually the climate changes, disastrous 

 erosion of the bare soil takes place, and when finally each community was 

 forced to move on to fresh clearings they left nothing but desert behind 

 them. Left to itself, first coarse grass, then undergrowth, then tropical 

 forest crept back, and in some cases was again denuded at an interval of 

 clearly not less than 2,000 years by another wave of population. 



One curious point in the history of these successive changes is that in 

 many lately re-afforested places in Central America the humus-inhabiting 

 Arthropods, which could not survive the heat, dryness, and sunlight of 

 the .period of cultivation, have not yet returned to their late home, while 

 such remnants of ancient forests as exist possess a rich humus-inhabiting 

 fauna. 



The pamphlet contains many picturesque details and concludes with a 

 note of warning against the harmful tendencies of some present-day 

 systems of American agriculture. — M. L. H. 



Vegetation of Sandy Seashores. By P. Olsson Seffer (Bot. Gaz. 

 vol. xlvii. (1909), No. 2, pp. 85-126; with 12 figs.).— The author details 

 many interesting observations as to air-temperature, air-moisture, analysis 

 of spray from the sea, soil temperature at various depths (ten tables), 

 mechanical analysis and chemical composition of sands, soluble salt 

 contents in coastal sand, &c. He also alludes to the effects of oscillations 

 of the coast line, to the influence of the wind and to man's intervention. 



The diurnal range of temperature amounted to as much as 25*6° C. 

 on Finland dunes and 24*3° at Perth, W. Australia. 



The influence of the salt spray from the sea was clearly brought out 

 in the case of an Australian Mesembryanthemum which was much 

 taller, and had longer leaves and less succulence in a wind-sheltered 

 position near the beach. On the other hand, the author could detect 

 no difference between specimens from the beach and others grown in the 



