304 GENETICS IN RELATION TO AGRICULTURE 



extensively in creating improved varieties. But before hybridization 

 was resorted to there were a dozen distinct color varieties which had 

 arisen by mutation. Besides color mutations there have occurred 

 spontaneous changes in flower form, flower size, and number of flowers 

 on the stem, in stature and habit of the plant and in season of bloom, 

 some of which are described below. 



Flower Color in Sweet Peas. The chronology and probable ancestry 

 of the color varieties of the sweet pea which appeared during the first 

 180 years of its horticultural history are shown in condensed form in 

 Table XLV. This summary is based upon Beal's excellent historical 

 review, from which citations to original sources have been obtained. 



Apparently the course of events was about as follows. From the 

 original type form there appeared first white mutations (Plate III, 3.) 

 If we call the simple flower-color factor complex CRB, in which C and R 

 are complementary factors producing red, and B an epistatic factor 

 which modifies that color to purple, then these mutations apparently 

 depended upon a change in either C or R to the recessive, white condition. 

 The Painted Lady variety, red instead of purple, shown in Plate III, 2, 

 appeared very soon after this, apparently as an independent mutation 

 in the factor B from purple. By the close of the eighteenth century 

 two other color types, black and scarlet, had been added to the list. 

 The wild form and Painted Lady are bicolors, that is, the wings are lighter 

 in color than the standard. The new color type scarlet (Plate III, 5,) 

 apparently resulted from a recessive factor mutation conditioning the 

 development of full color in the wings along with a certain intensification 

 of color in the standard. Black (Plate III, 6,) was probably also merely a 

 factor mutation for more intense pigmentation from the wild color type. 

 Early in the eighteenth century a "blue" form, var. caeruleus, was 

 described in the trade, but its genetic relationships have not been clearly 

 defined. Plate 111,8, which is taken to represent it has not been copied from 

 a particular variety as was done in the case of the other types. Further 

 additions shortly followed in the form of a "striped" variety, and of a 

 "yellow " variety. The latter (Plate III, 4) unquestionably originated as 

 a factor mutation from white, the former may have arisen as a factor 

 mutation in purple. Plants with primrose yellow flowers have since been 

 observed a number of times in white cultures, but never in red ones. 

 This practically closes the account of the origin of color mutations up to 

 the year 1880, after which time hybridization was resorted to extensively 

 in the creation of new varieties. 



Form and Size in Sweet Peas. The changes in form and size of flower 

 in the sweet pea have been no less striking than those in color, and they 

 have been responsible for a large portion of the popularity which it 

 enjoys. Today one can scarcely recognize in the favorite varieties of 



