THE ECOLOGY OP PLANTS. 455 



About one-fourth (about 70 species out of 300, of native 

 British annuals are cornfield weeds ; many of them extend 

 over the whole of the temperate regions, but they probably 

 all emigrated from central Europe or central Asia. Most of 

 our remaining wild annuals grow on rocks or hills, at the 

 seaside, and in other places where there is little competition 

 with perennials. That the annual weeds must have rich soil 

 and that they cannot compete on equal terms with perennials 

 is clearly seen in the succession of the vegetation which 

 springs up on a field allowed to remain fallow or on a piece 

 of cleared ground. 



During the first year after the clearing we get chiefly 

 annuals (e.g. Poppies, Charlock, Chickweeds, Goosefoots, 

 Red Dead-nettle, Spurges, Scentless Mayweed, several Speed- 

 wells, Scarlet Pimpernel, Sow-thistle, Shepherd's Purse, 

 Groundsel, Knotgrass, Fumitory). Next year the perennials, 

 some of which may have already got a footing among the 

 quicker- growing annuals, grow steadily and to a large extent 

 crush out the annuals ; perennials which do this effectually 

 include Nettles, Docks, White Dead-nettle, Plantains, Mil- 

 foil, Thistles, Daisy, Dandelion, Hawkweeds, etc., also such 

 shrubs as Brambles, and various G-rasses like Couch-grass, 

 Cock's-foot, etc. By the third or fourth year many of the 

 annuals have disappeared and the ground is largely occupied 

 by the perennials and a few strong biennials (e.g. Burdock). 

 The vegetation which settles in fallow or cleared land varies, 

 of course, with the factors of the habitat exposure, soil- 

 texture, moisture, etc. 



In studying cornfield weeds (in fields where cereals or other tall- 

 growing crops are cultivated) note (1) the weeds which grow low down, 

 often forming a thicket sheltered by the forest of tall corn stems, e.g. 

 Field Pansy, Chickweed, Speedwells, Corn Salads ( Valerianella, with 

 minute clustered blue flowers), Stork's-bill, Hop Medick, Hop Trefoil, 

 Black Medick, and many others, some climbing up the corn stems 

 (Fumitory, PolygoTwm convolvulus}, some appearing early before the 

 corn has grown up (Corn Pansy, Speedwells, etc. ) ; (2) the tall weeds 

 which grow up with the corn and usually flower and fruit at the same 

 time with it, e.g. Corn Buttercup, Corn Cockle, Bladder Campion, 

 Evening Campion, Charlock, Poppy, Hemp Nettle, Corn Mint, and 

 many others, mostly having erect main stems, few branches, and 

 narrow entire or divided leaves more or less upwardly directed ; 

 (3) the weeds at the edges and corners of the field, e.g. Nettles, 



