ADULT CHARACTERS IN 



SUNFLOWER SEEDLINGS 



T. D. A. CocKERELL, University of Colorado 



THE study of seedlings is obvi- 

 ously of practical importance. 

 We want to be able to recognize 

 the young plants coming up; to 

 know the different kinds of weeds, in 

 order to d£al with them at the earliest 

 possible moment. For such purposes, 

 it is suffici?nt to be able to distinguish 

 the genera and species in the seedling 

 stage, and we are not particularly con- 

 cerned with the varieties. When rais- 

 ing new varieties of simfiowers, how- 

 ever, we have had occasion to note the 

 variation in the seedlings of the species 

 Helianthiis annntis, and to consider its 

 meaning and importance. At the out- 

 set, we noticed that the coronaius 

 variety, with chestnut red on the rays, 

 could nearly always be distinguished as 

 a seedling by the purple tint of the 

 stalk and cotyledons. The stalk, or 

 more properly h^'pocotyl, is usually 

 deep purple, while the cotyledons show 

 more or less of the same color. This 

 enables the grower to pick out his red 

 sunflowers almost as soon as they are 

 up, and reject those which do not pos- 

 sess the desired character. Unfortun- 

 ately the distinction is not valid for the 

 vinous (wine-red) forms; why, we do 

 not at present know. More recently, 

 we have found various modifications of 

 the cotyledons, showing structural as 

 well as color differences. Four of 

 these are now figured, and may be 

 described thus: 



Fig. A, A.i April 21, 1916. Seed- 

 ling of var. coronatus, with one cotyle- 

 don strongly bi-lobed. At the angle 

 between the lobes, on the under side 

 (Fig. A^) is a sort of little pocket, sur- 

 rounded by a swelling. The hypo- 

 cotyl, margins of cotyledons, and a 

 median band on the bi-lobed cotyle- 

 don, are dark purple. The small first 

 leaves are hairy, and minutely speckled 

 with Durple. 



Fig. B, B.' April 23, 1916. Seed- 

 lings from Leonard Sutton of England, 

 from vinous plants with quilled rays. 



About half these seedlings show an 

 entirely new variation of the cotyledons, 

 which appear fiddle-shaped, with the 

 middle pinched in. They are not 

 really narrower in the middle, but the 

 margins are elevated (Fig. B\ cross- 

 section), giving the appearance shown. 

 There is a variable dark purple median 

 stripe, sometimes absent. On July 23 

 the plants were in flower, and were vin- 

 ous bi-color, mostly rather pale, with 

 normal rays. 



Fig. C. April 11, 1916. Seedling of 

 var. coronaius. The cotyledons have 

 very conspicuous dark purple bands 

 running down the middle, not reaching 

 the apex. The margins of the bands 

 are fimbriate toward the apex. 



Fig. D. April 19, 1916. Grown in 

 house. Seedlings of var. vinosus x 

 (anmtits coronatus x cucumerifolius) ; 

 that is to sa3^ one of the parents is a 

 hybrid between H. annuus and cucu- 

 merifolius. Cotyledons above entirely 

 dark plum color, small ; first leaves light 

 green, contrasting. April 22. Four 

 plants with same history now up, two 

 dark, two with green cotyledons. These 

 all set out in garden, and on May 6 the 

 cotyledons had grown considerably, 

 and were now green, the purple having 

 disappeared. First leaves light green. 



We may consider these variations 

 from two points of view. Are they 

 connected with adult characters? Are 

 they of any functional significance? 



As to the latter question, it is not to 

 be supposed that the modifications of 

 shape have any functional importance. 

 With regard to the color, the matter is 

 not quite so clear, but the green seed- 

 lings in the lot described under D grew 

 exactly as well and in the same manner 

 as the purple ones. It is not possible 

 to find any physiological advantage in 

 the dark color, apparently. Indeed, 

 Miss Wheldale, in her important new 

 work on "The Anthocyanin Pigments 

 of Plants," after devoting a chapter to 

 the physiological significance of antho- 



361 



