72 EXPERIMENTAL EVOLUTION LECT. 



become smaller. Such 'differences may be noticed 

 among all sorts of animals, from the highest to the 

 lowest. Gerard has noticed that bees transferred from 

 Burgundy to Bresse become larger in a generation ; A. 

 H. Curtiss has seen, in some places near the Potomac, 

 Bidens cernua acquire a height which is six times 

 the common average height of this plant, and he has 

 seen the same in Oxalis stricta ; C. Lemaire states in 

 D'Orbigny's Dictionary that, while cultivated hemp 

 grows no higher than a metre and a half in France, in 

 Piedmont it attains three and four metres ; and if 

 Italian stock is planted in France it rapidly reverts to 

 the small variety, in the course of two or three 

 years. Speaking of horses and of their dimensional 

 differences according to climate and environment, De 

 Quatrefages expresses himself as follows : " These 

 contrasts may be interpreted as due to the influence 

 which must be exerted on the first-named [Corsican 

 and Pyrenean stocks] by the stimulating and dry air 

 of the mountains, the frugal food with which they 

 must often be content, and, doubtless also, the hard 

 exercise which is rendered necessary by the roughness 

 of the soil. The others, on the contrary, [he refers to 

 the large heavy horses of the Bresse province,] always 

 immersed in a moist and heavy atmosphere, over-fed 

 with watery plants, and having none but easy work to 

 perform, must surely feel the effects of an environment 



