VARIETIES OF THE PLANT. 31 



Another cause, still greater, perhaps, and one that 

 has a more powerful effect in determining the shape of 

 the leaves and the peculiarities of the plant, is the cross- 

 fertilization of different varieties. From two varieties, 

 the one with a narrow leaf, and the other with a broad 

 leaf, by cross-fertilization may be produced one partak- 

 ing of the character of both. Planted on the same farm, 

 and even in the same field, they will produce some 

 modification of variety in the succeeding crop, although 

 the utmost pains may be taken to prevent this, by turn- 

 ing out the seed heads of the two varieties as far apart 

 as possible. Any one who has grown a few hundred 

 plants of Cuba tobacco, for domestic use, on a farm 

 where the heavy export tobacco is produced from the 

 Big Orinoco, the Medley Pryor, or the Beat-All, knows 

 that in the crop of the succeeding year many growing 

 plants will be found with the sweetish odor of the Cuba 

 tobacco, growing side by side with the heavy varieties. 



It is exceedingly important, therefore, in conse- 

 quence of the readiness with which the varieties mix, that 

 in order to keep a desirable variety from deterioration, 

 no two varieties shall be planted upon the same farm. 

 Hundreds of modifications of varieties have thus been 

 made. Darwin made some exceedingly interesting ex- 

 periments in the cross-fertilization and self-fertilization 

 of the tobacco plant, from which he drew the conclusion 

 that cross-fertilization from plants grown from the same 

 seed produces deterioration of variety, both in size and 

 weight. 



On the other hand, when a plant is cross-fertilized 

 with a totally different variety, grown under different 

 conditions of climate and culture, and on different soils, 

 the improvement was manifest, both in size and 

 weight. This improvement was shown in several ways, 

 "by earlier germination of the crossed seeds, by the 

 more rapid growth of the seedlings while quite young, 



