84 THE POPULAR SCIENCE MONTHLY. 



nature of the soil ; thus the couch-grass was ultimately spread over 

 all the plots, whether of sand, or of loam, or of lime, whether drained 

 or undrained. So also with Poa pratensis and Potentilla reptans. So 

 that the chemical and physical nature of the soil, as has been so often 

 shown in similar investigations, plays only a secondary part. 



As to the action of shade, it was found by Prof. Hoffmann that low- 

 growing plants, especially if annuals, disappeared rapidly, while taller- 

 growing plants, such as couch, Prunus Paclus, etc., survived. The 

 survival of certain plants, then couch, Aster, Potentilla, etc. is due 

 much less to external conditions than to the " habit " of the plant it- 

 self ; that is to say, to the facility the plant has of adapting itself to 

 varying external conditions, and thus of triumphing over others less 

 favorably endowed in this wise. 



The immediate source of victory lies in the powerful root-growth 

 Of the survivors, including under the general term " root " not only 

 the root proper, but the offshoots and runners which are given off just 

 below, or on the surface of the ground. Indeed, the latter habit of 

 growth is more advantageous to plants in such a struggle than the de- 

 velopment of the true root downward would be. Among those plants 

 where the roots were equally developed there were, nevertheless, ine- 

 qualities of growth, dependent, probably, on the greater need for light 

 in some species than in others, etc. 



It is clear from Prof. Hoffmann's experiments that, but for the con- 

 tinual use of the hoe, and the diligent extirpation of the weeds in our 

 fields, the stronger-growing ones would not only destroy our crops, 

 but also other weeds less vigorous than themselves. But they are not 

 sufficient to explain all the conditions of this complicated problem ; as 

 is shown by the fact that, in the district adjoining the locality where 

 Prof. Hoffmann's experiments were carried on, the predominant plants 

 are not the same as those which ultimately proved victors in the ex- 

 perimental beds. 



We may add that for two years a series of observations was car- 

 ried on in the gardens of the Royal Horticultural Society, at Chiswick, 

 with a view to ascertain how certain selected plants, twelve in num- 

 ber, and naturally growing in pastures, would be affected when grow- 

 ing by themselves, by the addition of manures of five , different de- 

 scriptions, and similar to those used at Rothamsted. In some cases the 

 results of these experiments were unsatisfactory, from circumstances 

 that need not be detailed here ; still a large body of facts was ac- 

 cumulated, and, with reference to the property by which certain plants 

 prove victorious in the struggle for life, it was clear that the natural 

 habit or organization of the plant was, cceteris paribus, the mainspring 

 of its success over its competitors. The several manures intensified or 

 deteriorated this peculiar organization, as the case might be, and thus 

 favored or impeded its growth accordingly. Popular Science Review. 



