Febeuaet 25, 1921] 



SCIENCE 



189 



the vibration is maintained. It also plays 

 under water ! 



I have written out the theory, which under 

 a certain assumption, shows that the sound 

 can not be simple harmonic, though periodic. 

 Pursuing the subject farther, I find that the 

 problem leads to an integro-difFerential equa- 

 tion of a new type, and non-linear. Being in 

 Paris in the summer of 1919 I wrote it out in 

 French, hoping to present it to the Academie 

 des Sciences, but took the precaution to show 

 it to M. Hadamard. When he saw it he threw 

 up his hands and exclaimed, " Vous avez resolu 

 cela ? " I replied, " ISTon, mais je I'ai pose," 

 bearing in mind one of his papers where he had 

 said that a problem was half solved when it 

 was "bien pose." I thought I deserved some 

 credit for that. So there it rests, half (or less) 

 solved. If any of your readers think they can 

 solve it, I am willing to divide the profits, or 

 KtJSos, with them. 



I am also indebted to Professor Barus for 

 the word " siffling," which I had thought a 

 Gallicism, but find that it is used by Chaucer. 

 Arthur Gordon Webster 



Olask University, 



variation in taraxacum 

 To THE Editor of Science : Since several 

 species of Taraxacum are parthenogenetic and 

 at the same time highly variable they have 

 looked like tempting material for the study of 

 certain phases of genetics. Moreover their 

 " polymorphy," as well as that of other par- 

 thenogenetic plants, has served as a partial 

 basis for well-known attempts to explain par- 

 thenogenesis as due to hybridization. 



As a matter of fact the degree of leaf dis- 

 section is correlated with the age of a given 

 rosette. The typical seedling leaf in both of 

 our common species (T. vulgar e, gray- fruited, 

 and T. Iwvigatum, red-fruited) tends to be 

 entire and smooth, with the plant producing 

 more dissected, and often more hairy, leaves as 

 it grows older. This would have been obvious 

 to students of the genus but for the confusing 

 fact that smooth, entire leaves are often found 

 on very old roots. If such cases are examined, 

 however, it will be found that the apparently 



juvenile leaves are borne on multicipital 

 branches of tender age. 



It is of course well known that the vigorous 

 production of blossoms after the second year 

 causes a radial splitting of the root crown in 

 seedling plants and the production of several 

 daughter rosettes upon the parent root. This 

 cleavage may extend through the length of the 

 root and produce a number of distinct indi- 

 viduals, but in any case the daughter rosettes 

 repeat the history of the parent seedling ro- 

 sette, so far as leaf characteristics and bloom- 

 ing habits are concerned. If the newly split 

 crown has been buried, the daughter rosettes 

 will be produced at the end of typical rhizomes, 

 often as much as six inches in length. Subse- 

 quent pressure renders these rhizomes quite 

 root-like. 



The above considerations clarify the inter- 

 esting results of a culture experiment reported 

 by Stork^ It is, moreover, not unprofitable 

 from the standpoint of taxonomy to inspect the 

 average herbarium collection of Taraxaca 

 while bearing in mind the correlations just 

 pointed out. Paul B. Sears 



University op Nebraska 



SCIENTIFIC BOOKS 



Pharmaceutical Botany, A Text-hooTc for 

 Students of Pharmacy and Science. Third 

 Edition. By Heber W. Toungken, A.M, 

 M.S., PI1.M., Ph.D., Professor of Botany 

 and Pharmacognosy, Philadelphia College 

 of Pharmacy. P. Blakiston's Son & Co., 

 Philadelphia. 1921. Pp. xix-f479. 238 

 illustrations and glossary. 

 This third edition of Dr. Toungken's excel- 

 lent text-book has all the satisfactory points 

 of the two preceding editions together with 

 an enhanced value to teachers of the subject 

 on account of the extensive improvements 

 made in it. By reason of its adoption as a 

 text in many academic institutions in addi- 

 tion to its very general use in the pharmacy 

 schools, the author has followed the tendency 

 already expressed in the second edition of 

 making it more suitable for general botanical 

 1 Bull. Torr. Bot. Club, 47 : 199-210, 1920. 



