No. 4.] CROSSING OF PLANTS. 31 



different places or under different conditions gives better 

 offspring than crossing between different plants grown in 

 the same place or under similar conditions ; and his researches 

 have also shown that, as a rule, flowers are so constructed as 

 to favor cross-fertilization. In short, he found, as he ex- 

 pressed it, that " nature abhors perpetual self-fertilization." 

 Some of his particular results, although often quoted, will 

 be useful in fixing these facts in our minds. Plants from 

 crossed seeds of morning-glory exceeded in height those from 

 self-fertilized seeds as 100 exceeds 76, in the first generation. 

 Some flowers from these plants were self-pollinated and 

 some were crossed, and in this second generation the crossed 

 plants were to the uncrossed as 100 is to 79 ; the operation 

 was again repeated, and in the third generation the figures 

 stand 100 to 68 ; fourth generation, the plants having been 

 grown in midwinter, when none of them did well, 100 to 86 ; 

 fifth generation, 100 to 75 ; sixth generation, 100 to 72 ; sev- 

 enth generation, 100 to 81 ; eighth generation, 100 to 85 ; ninth 

 generation, 100 to 79 ; tenth generation, 100 to 54. The aver- 

 age total gain in height of the crossed over the uncrossed was 

 as 100 to 77, or about 30 per cent. There was a corresponding 

 gain in fertility, or the number of seeds and seed-pods pro- 

 duced. Yet, as striking as these results are, they were 

 produced by simply crossing between plants grown near 

 together, and under what would ordinarily be called uniform 

 conditions. In order to determine the influence of crossing 

 with fresh stock, plants of the same variety were obtained 

 from another garden, and these were crossed with the ninth 

 generation mentioned above. The offspring of this cross 

 exceeded those of the other crossed plants as 100 exceeds 

 78, in height; as 100 exceeds 57, in the number of seed- 

 pods ; and as 100 exceeds 51, in the weight of the seed-pods. 

 In other words, crosses between fresh stock of the same 

 variety were nearly 30 per cent more vigorous than crosses 

 between plants grown side by side for some time, and over 

 44 per cent more vigorous than plants from self-fertilized 

 seeds. On the other hand, experiments showed that crosses 

 between different flowers upon the same plant gave actually 

 poorer results than offspring of self-fertilized flowers. It 

 is evident, from all these figures, that nature desires crosses 



