208 MASS MUTATIONS AND TWIN HYBRIDS OF 



the same hereditary conditions, even as in the crosses of the pale 

 mutant with the species. The specimen of lorea seems to be due 

 to a corresponding mutation in the ochracea, showing that this 

 mutability is not as wholly absent here as the results of self-fertili- 

 zation seemed to indicate. 



In all these crosses the lorea marks must be assumed to be reces- 

 sive to the grandiflora character. I have not made any second gene- 

 rations to decide this question, but the results of my crosses with 

 allied species will fill up this gap and show that in crosses with 

 lorea this type is split off, as a rule, in the second generation in pro- 

 portions which correspond to the law of Mendel. 



0. grandiflora mut. gigas (fig. 3) occurred in one specimen among 

 the 1180 plants of my cultures of 1915, pointing to a coefficient of 

 mutation of 0.1 per cent. This mutant attracted my attention in 

 May and was planted separately with some other eeemingly aber- 

 rant specimens. It opened its first flowers in the middle of August. 

 They were strikingly larger, with broad, thick petals, a thicker tube 

 of the calyx, thick filaments, anthers, and lobes of the stigma, and 

 a rich supply of pollen. The flower buds were almost conical and 

 the pollen was rich in quadrilateral grains, one of the characters of 

 the gigas mutants of allied species. The nuclei of the young buds 

 were investigated by my assistant Mr. C. van Overeem, who also 

 counted the chromosomes in the young roots of the seedlings of 

 the following year. The number was invariably 28, showing the 

 perfect analogy of this beautiful form with 0. Lamarckiana mut. 

 gigas and other giant mutants. 



From the self-fertilized seeds of this mutant I had a bed of 123 

 plants in 1916. They were uniform, with the exception of some 

 specimens of lorea and one ochracea. By May all of them had broader 

 and thicker leaves than 0. grandiflora, which was cultivated next 

 to it for comparison under exactly the same conditions. The leaves 

 of the young plants in June were 7 cm. broad, 20 cm. long, and a 

 deep, downy green. In July the height was 60—70 cm., but the 

 differences remained the same and very striking, the leaves of 0. 

 grandiflora being clearer green and only 4 cm. broad. The stems 

 were much stouter than in the species. During the flowering perod 

 the height of the plants exceeded that of the species only a little, 

 but all organs were much stouter. The internodes were shorter and 

 the number of leaves correspondingly larger. Over one-half of the 

 whole culture have flowered, the remainder being pulled out earlier 

 because unexpectedly the crowding of the plants became dangerous. 



