XIX.] SHORTENING OF SEASON OP GROWTH. 331 



give successive gain in yield, other things being 

 equal. This statement will apply to many garden 

 vegetables as well. Red peppers brought from the 

 southern United States give in Michigan a very small 

 yield the first year. The second year's crop is better, 

 and the third or fourth is fair to good. The season 

 of growth becomes so much shortened that the plant 

 can mature. "The races of melons, squashes and 

 gourds, which have long been cultivated in northern 

 Europe, are comparatively more precocious, and need 

 much less heat for maturing their fruit, than the va- 

 rieties of the same species recently brought from 

 tropical regions."* A single ear of precocious rice has 

 given rise to the only kind that can now be grown north 

 of the great wall of China. t (See also, Bretschneider 

 on the Study and Value of Chinese Plants, 44.) 



This shortening of the season of growth is not 

 confined to herbs. Trees mature earlier at the north 

 than at the south. They also start relatively earlier — 

 that is, at a lower temperature. "It occurred to M. 

 De CandoUe to test the matter. * * * ^^ some 

 time last winter he had branches sent him from Mont- 

 pelier of Populus alba, Carpinus Betulus, liriodendron 

 and catalpa. These were paired with similar branches 

 taken from trees at Geneva, and after a common so- 

 journ in a cool room long enough to make sure of 

 complete penetration by the same temperature, the 

 pairs were placed in glasses of water with some sand 

 at bottom, and kept in a warm room under exactly the 

 same conditions. * * * The result was that the 

 German trees leafed out first. In the case of the poplar, 



*Naudin, cited by Darwin, 1. c. 376. 

 tEncyclopedia Brit. 9th Ed. i. 86. 



