52 REVIEWS. 



have supposed that winged seeds were favourable to the dispersion of 

 species, but M. de Candolle's tables show a different result. In almost 

 every family enumerated, the per centage is in favour of naked or wingless 

 seeds, remarkably so in Dipsacece, where 11 per cent, of species with cal- 

 vous seeds are widely dispersed, while only 3 per cent, of those furnished 

 with pappus enjoy as wide a range. Among the Composite the propor- 

 tions are as 4*5 to 2*9 per cent, in favour of calvous seeds, by which it 

 should follow that daisies were twice as diffusable as thistles or dandelion. 

 A list is given of 117 species, which occupy very large areas, " at least 

 a third part of the surface of the globe." Out of these, 1 00 are natives of 

 Britain. Many of them extend over much more than the third part of the 

 earth's surface, but none appear to compass the whole earth, however wide 

 their extent. " The Stellar ia media (chick weed), for example, which en- 

 dures very severe climates, and easily becomes naturalized in temperate 

 regions, is found neither at Melville Island, nor in Labrador, nor under the 

 Equator." "Nettles themselves, which one looks upon as accompanying 

 man, do not support, like him, the extremes of cold and heat ; they are 

 wanting in Labrador, Melville Island, as well as on the plains of the torrid 

 zone. The Portulaca oleracea, Sonchus, Lamium amplexicaule, Chenopo- 

 dum album, Cynodon Dactylon — plants that may be looked on as univer- 

 sally diffused, so common are they, and so easily naturalized — do not pene- 

 trate into the extreme northern climates. One alone, the Sonchus olera- 

 ceus, is, perhaps, so organised as to endure all climates, from the equator to 

 the pole ; but it needs a cultivated soil or rubbish ; and such stations are 

 wanting, and always will be so toward the extreme north. Thus, I repeat, 

 no phanerogamous plant is or can become a cosmopolite in the absolute 

 sense." The number found to occupy half the globe is extremely limited, 

 only 18 being enumerated out of the 117 first named. Many of the most 

 widely dispersed are either purely aquatic or frequent very moist situa- 

 tions ; 14 or 15 species are natives of Very dry places, and from 25 to 30 

 are chiefly found in cultivated ground. Many littoral species, which 

 would have found a place in the lists, if the calculations had been based 

 on parallels of latitude or longitude, are excluded, because, though widely 

 dispersed geographically, they extend too short a distance from the shore 

 to form large areas of distribution. No tree or shrub figures in the list* 

 The Thymus serpyllum is the most ligneous plant, if we can call it an 

 " undershrub." Of the species enumerated 47 are annuals, 3 biennials, and 

 66 perennials ; 73 are dicotyledons, and 44 monocotyledons — that is, in 

 the proportion of 62 per cent, dicotyledons to 38 per cent, monocotyledons. 



