THE MARKING FACTOR IN SUNFLOWERS 



T. D. A. COCKERELL, 



Universitv of Colorado, Boulder, Col. 



1AST \-car, working on the coloring 

 matters in sunflowers, I made 

 J the unexpected discovery that 



the rays of a number of perennial 

 species contain a substance which turns 

 bright scarlet or \-ermillion in caustic 

 potash soliUion. The annuals gi\'e no 

 such reaction, and thus it is evident that 

 although the visible colors in life may be 

 exactly the same, there is still something 

 fundamentally different, only revealed 

 by a chemical test. 



Another class of hidden characters has 

 to do with the markings of those 

 varieties which assume a red color. 

 In the ordinary orange-rayed sunflowers 

 it is often possible to detect a certain 

 deepening of the color toward the base 

 of the rays; sometimes this is quite 

 conspicuous. Photographs of such 

 flowers, taken without a color screen, 

 accentuate this effect, and produce the 

 ajipearance of strongly bicolorcd rays. 

 A \'cry remarkable instance of this sort 

 was discovered by G. N. Collins in 

 Bidens heterophylla, and published, with 

 good illustrations, in Plant World, 

 November, 1900. No species of wild 

 sunflower has red rays, and yet in the 

 red-ra\'ed varieties developed under 

 culti\-ation, or very rarely found wild 

 as single sjxjrts, the distriliution of the 

 red is controlled by "marking-factors," 

 which existed jjrior to and indepcnd- 

 tiitl\' of the color-development through 

 which they arc made manifest. The 

 indejK'ndcnt existence of these marking- 

 factors is shown not only by their 

 behavior in heredity, but also by their 

 partial or faint ai)pearanee in the orange 

 (wild) forms, and ihcir revclalion 

 thn)ugh ])h()tography. 



In the common garden sunflower, 

 liclianihns atnutits, or rather the series 

 of cultivated forms we have obtained 

 through crossing the original wild red 

 sjHjrt {H. annuus lenticularis var. coro- 

 natus) with garden varieties, the mark- 

 542 



ing-faetors form i\ quite definite system. 

 Their independence of the shade of 

 color is shown by the fact that the 

 chestnut-red {coronatus) and wine-red 

 ivinosiis) groups afford exactly parallel 

 series of types. The commonest form 

 (\^ar. bicolor) has the basal half or more 

 of the rays dark (chestnut or wine-red) 

 and the apical part yellow or orange in 

 the chestnut forms, primrose-yellow or 

 very pale yellowish in the wine-red. 

 Frequently, however, the base is pale 

 (var. zonatus), and the red forms a ring 

 around the head, crossing the middle of 

 the ra}'s. When the pattern-factor is 

 absent, the whole ray is colored, 

 chestnut or wine-red, as the case may be. 

 Such foiTns frequently show yellow at 

 the extreme base, and sometimes this 

 becomes a definite spot or patch. In 

 an occasional form there are two spots 

 of color, either chestnut or vinous, one 

 on each side of the basal part of the ray ; 

 the rest of the ray being orange or pale. 

 (Fig. C). This I call var. maculatus. 

 In the vinous or primro.se-\'cllow it is a 

 very pretty thing. 



I was ready to suppose that this 

 series of patterns would be found, quite 

 the same, in all annual sunflowers which 

 could be colored red. It turns out, 

 however, that this is not true; that 

 Hcliaiithus cticumerifolitis has a very 

 diflercnt set of ])atterns. Some years 

 ago M. Herb of Naples sent out what 

 he called Helianthus cucumerifolins pur- 

 ptireus, a form with more or less red on 

 the rays. The seeds first distributed 

 jjroduccd very unsatisfactory plants, 

 with very little red, and that dingy; but 

 M. Herb ]jcrsevered, and this year we 

 have seme very well-colored \-arietics 

 raised from seed which he kindh' sent. 

 The i)attems are on the whole very 

 different from tho.se of II . ou\iniis. In 

 the earh' cultures a common form 

 (illustrated in HerlVs catalogue for 1913) 

 had the color confined to abcnit a fourth 



