might kill back a plant already at the limit of its natural range, or a warm summer, by ripening abundance of its seed, might result in its slight advance. The general effect of human operations has been to lessen competition and increase suitable habitats by the destruction of the native vegetation which occupied them, and this has resulted in a general advance of a large number of species. What renders the study of this advance so difficult is the fact that on all disturbed land the truly native plants which have been ousted are striving side by side with the immigrants to regain their former territories; and it is now often very difficult to disentangle them: to separate the sheep from the goats. If only we could have had a Watson’s “Topographical Botany” written five thousand years ago, before our restless race began to mess up the vegetation! However, as has been said, what we have lost on one side we have gained on another. On every side bright immigrants meet the eye. Our old buildings and quarries often blaze with the Red Valerian (_Kentranthus ruber_) and Wallflower (_Cheiranthus Cheiri_); in fields Poppies of various kinds, Corn Cockle (_Lychnis Githago_), and Corn Blue-bottle (_Centaurea Cyanus_) add a glory to the rich green or gold of the cereals; dry banks and gravelly places are decorated with species of Melilot (_Melilotus_), Chamomile (_Anthemis_), Knapweed (_Centaurea_), and many others. The flora of harbours and docksides is often as cosmopolitan as the sailors of the ships by whose agency it came there; and the unfamiliar weeds--the gipsies and tramps of the plant world--which we encounter on roadsides, rubbish-heaps, and railway stations lend an additional interest to our botanical rambles.