OENOTHERA GRANDIFLORA AIT. 227 



this corresponds as exactly as might be expected to our ex- 

 planation. Thus we find: 



I 50 per cent pure x Lamarckiana = 25 per 

 \ cent ovata + 25 per cent brunnea 

 O. grandiflora x Lamarckiana = ) 50 per cent ochracea x Lamarckiana = 25 



f per cent ovata + 25 per cent lutea 



This formula may be considered to explain the empirical results 

 of our table, since it gives 50 per cent ovata and 25 per cent of each 

 of the other hybrids. The empirical figures were 52, 23, and 21 per 

 cent, as just mentioned. 



We may go still one step farther and introduce into our con- 

 sideration the property of Lamarckiana to produce the twin hybrids, 

 laeta and velutina. These are found, on the average, in about equal 

 numbers. Our formula now becomes: 



(x laeta =25 per cent ovata 

 1 50 per cent pure |xvelutina=25 per cent brunnea 

 O. grandiflora X La- ) 

 marckiana= ) (x laeta =25 per cent ovata 



f 50 per cent ochracea ( x velutina=25 per cent lutea 



It is easily seen that this formula opens a deeper insight into the 

 whole phenomenon of twin and triple hybrids. This point will be 

 discussed further at the end of this paper. 



0. Lamarckiana lata x 0. grandiflora. — I made this cross twice 

 in 1914 and 1915 and cultivated the first generation in 1915 and 

 1916, respectively. In the boxes it was clear that besides the hybrids 

 described for the parent species, specimens with the type of 0. 

 lata were present. They had the broad leaves with rounded tops 

 which are so characteristic of this mutant. They were planted 

 separately and developed their typical marks during the summer. 

 Their stems remained low and flexible, the foliage was dense, the 

 petioles short, the blades full of bubbles and paler green than in the 

 mutant from Lamarckiana. The flowers and fruits were almost 

 like those of this mutant, but there was plenty of pollen, and the 

 artificial self-fertilization gave a good supply of seeds. I counted 

 (in 1915) 18 lata among 30 plants, and in the next year 24 among 

 76; together 42 among 106, or about 40 per cent, a figure which 

 does not differ essentially from the hereditary percentages of 0. 

 Lamarkiana mut. lata. The remaining plants were mostly (41) 

 ovata, with some lutea and some brunnea, some dwarfs, and some 

 other mutants of different types. Thus we see that this cross gave 

 exactly the results that might be expected. 



In 1916 I sowed the seeds of three self-fertilized specimens of the 



