708 



SCIENCE 



[N. S. Vol. XL. No. 1037 



Dr. Johannes Meisenheimer, associate pro- 

 fessor at Jena, has been elected professor of 

 zoology at Leipzig, to succeed the late Pro- 

 fessor Chun. 



Dr. Paul Koebe, associate professor at 

 Leipzig, has been elected professor of mathe- 

 matics at Jena, as successor of Professor 

 Johannes Thomae. 



DISCUSSION AND COSEESPONDENCE 

 SUNFLOWER PROBLEMS 



Professor Bateson, in his British Associa- 

 tion address (Science, Aug. 28, 1914, p. 300), 

 has raised the question whether the red sun- 

 flower may not owe its chestnut color to the 

 loss of an inhibitor, instead of the positive 

 addition of a factor for red. Are all yellow- 

 rayed sunflowers potentially red, but prevented 

 from becoming so by something which "stops 

 down " the series of chemical processes which 

 would produce redness? 



So far as I can determine, the cultivated 

 Melianthus annuus is derived from the wild 

 M. lenticularis, which has a dark disc and 

 orange rays. The disc florets of this plant 

 have small triangular lobes, which are a sort 

 of dull wine red owing to an abundance of 

 anthocyan pigment. The rays are orange, 

 without red. The disc bracts have dark red 

 ends. There is evident anthocyan pigment in 

 the stem, producing a mottled effect. Thus, 

 it is clear that the kind of pigment which 

 characterizes the red sunflower is rather abun- 

 dantly present in the wild plant, although it 

 does not invade the rays. Occasionally, how- 

 ever, the rays show a little red. At Longmont, 

 Colorado, August 30, 1914, I found a plant of 

 H. lenticularis having the middle third of the 

 rays beneath with the apical half variably 

 light brov5nish-red. Microscopic examination 

 showed cells with anthocyan, which became 

 redder with acid. On the upper side, the rays 

 were entirely orange as usual. In the red 

 sunflowers, it is this middle tract of the under 

 side of the rays which is generally especially 

 heavily pigmented. Had this Longmont plant 

 a special " factor for red," or had some of the 

 effects of the normal reddening factor of the 



disc florets spilled over, as it were, on to the 

 rays? In our red sunflowers, we find that the 

 heterozygous forms may be very richly colored. 

 Nevertheless, they may be almost wholly yellow- 

 rayed. The most extreme case of this sort 

 is a plant grown this year, which has very 

 purple stems and branches, but the very rich 

 orange rays apparently wholly without red, 

 though a lens shows a little scattered red. 

 In this case it would seem natural to think of 

 the red being inhibited. However, the appear- 

 ance of yellow-rayed heads at the end of the 

 season on heterozygous more or less red-rayed 

 plants suggests not so much the late develop- 

 ment of a special inhibitor, as the failure 

 under adverse conditions of the color-producing 

 mechanism. In other words the " inhibitor " 

 here is nothing more than the withdrawal of 

 the needful stimulus. 



The monoeephalous garden sunflowers have 

 the disc yellow, the red having disappeared 

 from the disc florets. The same variation 

 occurs from time to time in the related wild 

 species (e. g., the variety phenax of H. peiio- 

 laris). Dark disc is strictly dominant or 

 epistatic to yellow. Here we naturally speak 

 of the loss of a factor; but carrying the inhib- 

 itor postulate a little farther, we can assume 

 that we have here a second inhibitor, acting 

 upon the disc, only operating when the plant 

 is homozygous for it. A supposition of this 

 sort is certainly fatiguing to the imagination. 



In homozygous red-rayed sunflowers, the 

 pigmentation may be intense.^ We not only 

 have the form (var. ruberrimus, nov.) with 

 the rays deep chestnut red all over; but this 

 year we obtained one (var. niger, nov.) with 

 the rays practically black above, slightly red 

 apically, though beneath they showed on one 

 side a streak of orange. (The orange streak 

 on one side, not always the same side, beneath, 

 is a regular character of the very red varieties. 

 I am not at present able to explain this asym- 

 metry, unless it has to do with the manner 



1 It is singular that the pigmentation of the seed 

 (fruit) follows quite different lines. Sutton's tall 

 primrose variety of S. annuus has long black seeds, 

 and in a cross with brown-seeded varieties, the 

 seeds of Fj come broad and dark brown. 



