322 CEREAL PLANTS. 



Chap. IX. 



three to four months. 58 Peter Kalm, 59 who particularly attended to this 

 plant, says, that in the United States, in proceeding from south to north 

 the plants steadily diminish in bulk. Seeds brought from lat. 37° in Vir- 

 ginia, and sown in lat. 43°-44° in New England, produce plants which 

 will not ripen their seed, or ripen them with the utmost difficulty. So it 

 is with seed carried from New England to lat. 45°-47° in Canada. By 

 taking great care at first, the southern kinds after some years' culture 

 ripen their seed perfectly in their northern homes, so that this is an ana- 

 logous case with that of the conversion of summer into winter wheat, and 

 conversely. When tall and dwarf maize are planted together, the dwarf 

 kinds are in full flower before the others have produced a single flower • 

 and in Pennsylvania they ripen their seed six weeks earlier than the 

 tall maize. Metzger also mentions a European maize which ripens its 

 seed four weeks earlier than another European kind. With these facts 

 so plainly showing inherited acclimatisation, we may readily believe Kalm 

 who states that in North America maize and some other plants have 

 gradually been cultivated further and further northward. All writers 

 agree that to keep the varieties of maize pure they must be planted 

 separately so that they shall not cross. 



The effects of the climate of Europe on the American varieties is highly 

 remarkable. Metzger obtained seed from various parts of America, and. 

 cultivated several kinds in Germany. I will give an abstract of the 

 changes observed 60 in one case, namely, with a tall kind (Breit-korniger 

 mays, Zea altissima) brought from the warmer parts of America. During 

 the first year the plants were twelve feet high, and few seeds were perfected ; 

 the lower seeds in the ear kept true to their proper form, but the upper 

 seeds became slightly changed. In the second generation the plants were 

 from nine to ten feet in height, and ripened their seed better ; the depression 

 on the outer side of the seed had almost disappeared, and the original 

 beautiful white colour had become duskier. Some of the seeds had even 

 become yellow, and in their now rounded form they approached common 

 European maize. In the third generation nearly all resemblance to the 

 original and very distinct American parent-form was lost. In the sixth 

 generation this maize perfectly resembled a European variety, described 

 as the second sub-variety of the fifth race. When Metzger published his 

 book, this variety was still cultivated near Heidelberg, and could be distin- 

 guished from the common kind only by a somewhat more vigorous growth. 

 Analogous results were obtained by the cultivation of another American 

 race, the "white-tooth corn/' in which the tooth nearly disappeared even in 

 the second generation. A third race, the l ' chicken-corn," did not undergo 

 so great a change, but the seeds became less polished and pellucid. 



These facts afford the most remarkable instance known to me 

 of the direct and prompt action of climate on a plant. It might 



58 Metzger, ' Getreidearten,' s. 206. have consulted an old English MS. 



59 * Description of Maize,' by P. Kalm, translation. 



1752, in ' Swedish Acts,' vol. iv. I "o < Getreidearten,' s. 208. 



