556 



SCIENCE 



[N. S. Vol. LIII. No. 1381 



lowing promotions have been made: Dr. C. 

 B. Bazzoni to be professor of physics, Dr. 

 George Gailey Chambers and Dr. Howard 

 Hawks Mitchell to be professors of mathe- 

 matics and Dr. Karl Greenwood MiUer to be 

 assistant professor of psychology. 



DISCUSSION AND CORRESPONDENCE 



THE GEOGRAPHICAL DISTRIBUTION OF 

 HYBRIDS 



It is often assumed by systematic botanists 

 in this country that natural hybrids between 

 species can only exist within the common range 

 of the parent species. This opinion has been 

 emphasized in a caustic criticism of Brainerd 

 and Peitersen's recent article entitled " Black- 

 berries of 'Nevr England — their classifica- 

 tion." 1 In the article cited,- the following 

 expression appears: 



... no one, not specially forewarned or gifted 

 with remarkable intuition, finding Suhus frondi- 

 sentis {"S. pergratus X setostis") superabundant 

 dn Coos County, New Hampshire, B. glandioaulis 

 (" B. allegheniensis X sentosus") in the thickets 

 of Prince Edward Island, where B. setosus is un- 

 known, or B. arenicola ("B. Baileyanus X fron- 

 dosus") dominant on dry barrens of Nova Scotia 

 ■ where B. Baileyanus is unknown and where B. 

 frondosus is represented only by B. recurvans, can 

 guess in which key to trace his species. 

 A number of similar quotations might be cited 

 from the same source all involving the nega- 

 tion of the possibility of the occurrence of a 

 hybrid beyond the range of the parent species. 



It would seem reasonable to appeal to the 

 better known floras of Europe in a case of this 

 kind, and no one can perhaps be quoted with 

 more effect on this important subject than An- 

 ton Kerner von Marilaun. In the second vol- 

 ume of his classic " Pflanzenleben," as well as 

 in the " Osterreichische botanische Zeits- 

 chrift" (Vol. 21 (1871)), this distinguished 

 author has cited a large number of cases of 

 natural hybrids. 



Perhaps the most interesting example in 

 this connection is the hybrid Nuphar inter- 

 medium which is a cross between Nuphar 



1 Vermont Agricultural Experiment Station, 

 Bulletin 217, Burlington, Vermont. 

 . 2Ehodora, Vol. 22, pp. 185-191. 



luteum and Nuphar pumilum, found dis- 

 tributed from the Black Forest and the 

 Vosges northward into Russia and Lapland. 

 In the southern part of its range, the hybrid 

 is rarer and less fertile than it is further 

 north. It is capable of extending its latitude 

 northward of the range of both the parent 

 species. Parallel cases are supplied by hy- 

 brids of Epilohium, Brunella, Primula, Li- 

 naria, Rumex, Micomeria, Pulsatilla, etc. 

 In these various genera Kerner describes hy- 

 brids between wild species which often occur 

 beyond the range of one or both of the parent 

 species. Since the data supplied by Kerner 

 on this subject can scarcely be questioned, it 

 would appear that the absence of one or both 

 of the parent species of a supposed hybrid in 

 a given region is no valid argument against 

 the hybrid origin of such an intermediate 

 form. We have apparently still much to learn 

 from our European colleagues both as regards 

 accuracy and breadth of view in the matter 

 of geographical distribution of hybrids. In 

 the light of the above it does not appear neces- 

 sary that the statements of Brainerd in re- 

 gard to probable natural hybrids of Buhus 

 should be accorded less credence and respect 

 than have been given to his classic results in 

 the case of natural hybrids in the genus Viola. 

 E. C. Jeffrey 

 Harvard XJniversitt 



! 



STAR DIAMETERS 



To THE Editor of Science: Keferring to 

 the communication of Professor Eessenden 

 concerning star diameters (Science, March 

 25, 1921, page 287-8), allow me to say that it 

 does not seem possible that the measured 

 diameter of Betelgeuse is affected by a gravi- 

 tational displacement. In the first place, there 

 are stars, of solar type for example, in. 

 connection with which the conditions would 

 seem to be far more favorable for such a dis- 

 placement and yet these objects show no ap- 

 preciable disk. Further, we know that light 

 reacts to a gravitational field in such a man- 

 ner that there is no permanent acceleration 

 in the direction of propagation. This fact re- 

 duces the possibility of a displacement to a 



