3 2o PLANT-BREEDING 



uents, since the yellow spot is evidently due to a separate 

 unit. 



If, now, we cross the red and the white types, we get, 

 according to the ordinary rules, hybrids that bear the 

 marks of the species and not those of the variety. But in 

 the second generation a splitting occurs, and it is this split- 

 ting which frees the units from one another. A complete 

 analysis has not as yet been made, but some constituents 

 have been separated and have proven to be real units. Of 

 course, only some of the hybrids have but one unit in a pure 

 condition, others having groups of two or three or even more 

 of them in all imaginable combinations. But the more 

 simple forms are easily recognizable among the throng. In 

 the first place they give proof of the independence of the red 

 and yellow colors. A pure yellow form exists, lacking all 

 of the red. It has two units of color, the one being the spot 

 on the under lip, already mentioned, and the other the general 

 tinge. The red dye is also produced by at least two units, 

 one of them being a fleshy color, equally distributed in all 

 parts of the corolla, except the yellow spot, and the other 

 being of a bright color, but limited to the lips. It is a type 

 called Delila, and distinguished by its colorless tube. As 

 is easily seen, the combination of these two units gives the 

 dark lips and the pale tube of the original species, and this 

 not only theoretically but also experimentally whenever the 

 two constituents are combined by crossing. 



In the same way the colors and color- designs of other 

 flowers may be analyzed and their component units sepa- 

 rated. The most obvious means for almost all cases is the 

 crossing of the species which has all the units, with the white 

 variety in which they are absent or at least latent. Such 

 crosses usually result in the desired splitting. A most beau- 

 tiful instance may now be mentioned. It is the separating 

 of the dark central spot of the opium-poppies from the red 



