Bursa bursa-pastoris and Bursa heegeri biotypes and hybrids, by George Harrison Shull.

Tür:

Kitap

Yazar:

George Harrison Shull

Yayın yılı:

1909

Yayıncı:

Carnegie Institution of Washington,

cations of the old ones, as may be necessary for the interpretation of the observed facts of evolution.Among* the species now being-studied, one that has very early yielded results of interest in this connection is the common shepherd' s-purse of our dooryards.Bursa btirsa-pastoris (L.) Brjtton.Bursa iCapsella) biirsa-pastoris is known to the taxonomist as an exceed- ingfly variable species, which seems to have been brougfht to this country from Europe, but which is now naturalized and almost universally distributed throug-hout the North Temperate zone.So striking-ly different, qualita- tively, were the characters of different individuals observed growing-side by side in nature that it was difficult to believe that they all belong-ed to a sing-le series of fluctuating: variations, and when the opportunity offered to make pedigfree-cultures this species at once sug-gested itself as favorable material.This thoug-ht was based not alone upon its apparent polymorph- ism, but also upon its hardiness, ease of culture, and the impossibility of its having-been subjected to any of the artificial conditions of isolation, crossing-, etc., which are usually thought to render plants of economic value unfit to gfive information regarding-the behavior of plants in nature.No one has ever attempted to "improve" the shepherd 's-purse, and althougfh its rapid extension over its present gfreat rang-e is undoubtedly dependent upon the ag-ency of man, both in supplying-suitable habitats and more…

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