266 SUMMARY OF MEASUREMENTS. CHAP. VIL 



intercrossed plants of the same stock were to the self- 

 fertilised plants of the corresponding fifth generation 

 in fertility only as 100 to 86. 



Although at the time of measurement the plants 

 raised from the cross with the fresh stock did not 

 exceed in height or weight the intercrossed plants of 

 the old stock (owing to the growth of the former not 

 having been completed, as explained under the head 

 of this species), yet they exceeded the intercrossed 

 plants in fertility in the ratio of 100 to 54. This fact 

 is interesting, as it shows that plants self-fertilised 

 for four generations and then crossed by a fresh stock, 

 yielded seedlings which were nearly twice as fertile as 

 those from plants of the same stock which had been 

 intercrossed for the five previous generations. We 

 here see, as with Eschscholtzia and Dianthus, that the 

 mere act of crossing, independently of the state of the 

 crossed plants, has little efficacy in giving increased 

 fertility to the offspring. The same conclusion holds 

 good, as we have already seen, in the analogous cases of 

 Ipomoea, Mimulus, and Dianthus, with respect to height. 



(10.) Nicotiana tabacum. My plants were remark- 

 ably self-fertile, and the capsules from the self-fertilised 

 flowers apparently yielded more seeds than those which 

 were cross-fertilised. No insects were seen to visit the 

 flowers in the hothouse, and I suspect that the stock 

 on which I experimented had been raised under glass, 

 and had been self-fertilised during several previous 

 generations ; if so, we can understand why, in the course 

 of three generations, the crossed seedlings of the same 

 stock did not uniformly exceed in height the self-ferti- 

 lised seedlings. But the case is complicated by indi- 

 vidual plants having different constitutions, so that some 

 of the crossed and self-fertilised seedlings raised at the 

 same time from the same parents behaved differently. 



