906 



SCIENCE 



[N. S. Vol. XL. No. 1042 



acter and tliose laclcing it grows progressively 

 greater witli each factor added. 



The practical value of the principle may 

 prove to be considerable as it serves to explain 

 cases in vsrhich a character dominant in F^ 

 almost completely disappears in F„, and in 

 which an apparently non-mendelian result is 

 obtained involving a reversal of dominance. 



For supposing that a certain character, x, 

 depended for its visible manifestation upon 

 the simultaneous presence in the zygote of 

 20 factors which we may designate as A, B, 

 C . . . T. Then if an animal possessing this 

 character and the above mentioned factors is 

 crossed with one from a race lacking all these 

 ■•^actors, Fj would all he of the formula Aa 

 Bh Cc . . . Tt. All would develop the char- 

 acter in question since all had a single repre- 

 sentation of the twenty factors. If, however, 

 these F^ animals were ired inter se F, would 

 give approximately only one animal in Sllf 

 which had the character in question. If only 

 a small number of F, were raised the char- 

 acter might well be thought lost and perhaps 

 not truly inherited by F^. 



An entirely different result would, of course, 

 be obtained if the factors in question needed 

 to be present in all the gametes of the zygote 

 in order for the character to be visibly mani- 

 fested. In such a case as this none of F, would 

 show the character, and its reappearance in F, 

 would follow the ordinary rules of mendelian 

 segregation and recombination. 



This note is merely offered in the hope that 

 it may be of use in the explanation, on a Men- 

 delian basis, of certain results which might 

 otherwise be offered as examples of non-men- 

 delian inheritance. C. C. Little 



EussET Institution, 

 Harvard University 



the structure of the cotton fiber 

 In any kind of cotton the typical fiber, that 

 is the one in which all the essential parts may 

 be determined, can be found in rare cases. For 

 this reason the structure of an ideal fiber can 

 be inferred only from a series of studies of 

 fibers in successive stages of development. 



By subjecting such fibers to certain chem- 

 ical and bacteriological treatments and then 

 studying them under the microscope, we found 

 that the typical cotton fiber consists of the 

 following parts : 



1. The outer layer or the integument. 



2. The outer cellulose layer. 



3. The layer of secondary deposits. 



4. The walls of the lumen. 



5. The substance in the lumen. 



1. The outer layer or the integument is the 

 incrusting layer and forms the cementing 

 material of the fiber. Its chemical structure 

 is not an homologous one, but is a mixture of 

 components, some soluble in alcohol, some in 

 ether, and some in water. The components are 

 cutinous, pectinous, gummy, fatty and other 

 unidentified bodies. 



2. The outer cellulose layer is in its struc- 

 ture a distinct spiral, consisting of a limited 

 number of component fibers, perhaps of one or 

 of two. The structure of this layer is deter- 

 mined under the microscope from a longi- 

 tudinal section of the fiber after the latter has 

 been subjected to a series of chemical and 

 bacteriological treatments. Careful treatment 

 of some of the fibers by cuprammonia will 

 show under the microscope this spiral. There 

 is some evidence to show that this spiral con- 

 sists of impure cellulose. 



3. The layer of secondary deposits seem? to 

 be made up of component fibers which in no 

 case have shown a spiral structure. Unlike 

 the fibers of the above described layer, thgse 

 components are from about five to ten in num- 

 ber and run with some irregularities along 

 the length of the fiber. 



4. The structure of the layer forming the 

 walls of the lumen is a spiral much the same 

 as the outer spiral, but differs from it greatly 

 in its chemical composition. This is deter- 

 mined from a microscopical study of the fiber 

 while under a cuprammonia treatment. 



5. The substance in the lumen is structure- 

 less and, as is proven by a microscopical test, 

 is of a nitrogenous nature. 



B. S. Levine 

 The Biological Laboratory, 

 Brown University 



