320 FERTILITY OF CROSSED CHAP. IX 



These casos show us how greatly superior in innate 

 fertility the seedlings from plants self-fertilised or 

 intercrossed for several generations and then crossed 

 by a fresh stock are, in comparison with the seedlings 

 from plants of the old stock, either intercrossed or 

 self-fertilised for the same number of generations. The 

 three lots of plants in each case were left freely ex- 

 posed to the visits of insects, and their flowers without 

 doubt were cross-fertilised by them. 



This table further shows us that in all four cases the 

 intercrossed plants of the same stock still have a 

 decided though small advantage in fertility over the 

 self-fertilised plants. 



With respect to the state of the reproductive organs 

 in the self-fertilised plants of the two last tables, 

 only a few observations were made. In the seventh 

 and eighth generation of Ipomoea, the anthers in the 

 flowers of the self-fertilised plants were plainly smaller 

 than those in the flowers of the intercrossed plants. 

 The tendency to sterility in these same plants was 

 also shown by the first-formed flowers, after they had 

 been carefully fertilised, often dropping off, in the 

 same manner as frequently occurs with hybrids. The 

 flowers likewise tended to be monstrous. In the 

 fourth generation of Petunia, the pollen produced 

 by the self-fertilised and intercrossed plants was 

 compared, and there were' far more empty and shrivelled 

 grains in the former. 



Relative Fertility of Flowers crossed with Pollen from a 

 distinct Plant and with their own Pollen. This heading 

 includes flowers on the Parent-plants, and on the crossed 

 and self -fertilised Seedlings of the first or a succeeding Ge- 

 neration. I will first treat of the parent-plants, which 



