August 2, 1907] 



SCIENCE 



151 



The two force vectors q^ and g„, with their 

 direction cosines, Aj, im, yj, and A,, /j.^ y,. 



The two intersection curves rws^ and rws^ 

 with the reciprocal wave surface. 



The two reciprocal wave fronts rivf^ and 

 rwf,. 



The two reciprocal wave normals or recip- 

 rocal velocities, w/, w/, and their direction 

 cosines, Z/, m/, n/ and ?,', m,', n„'. 



The two vectors ;•/ and r/ of the reciprocal 

 wave surface and their direction cosines, 

 I, m, n. 



All the right angles are indicated and the 

 important angle 8, made by the force vector, 

 is shown in one case. 



Clearness is given to the diagram by pla- 

 cing the plane normal to the observer's line of 

 sight. The planes y^, Wj and m., y^ are at right 

 as the auxiliary vectors show. 



Naturally the above method is even more 

 pertinent to the modern methods of vector 

 analysis. The diagrams, like the computa- 

 tions, gain in simplicity. And yet it is just 

 here that authors are peculiarly unwilling to 

 fix the ideas of the student to a definite case. 

 Demonstrations in themselves admirably lucid 

 become confused in effect, because the reader 

 is all the while drifting in the haze of the 

 absolute generality of the statement of the 

 premises. Carl Barus 



A PRELIMINARY NOTE ON THE CHROMOSOMES OF 



CENOTHERA LAMARCKIANA AND ONE OF ITS 



MUTANTS, O. GIGAS 



The exceptional opportunities offered at 

 this station for a study of inheritance as 

 manifested in the germ cells of the (Enotheras 

 led me to undertake a study of the chromo- 

 somes of (Enothera Lamar ckiana, its mutants 

 and hybrids. 



The work was begun after the flowering 

 season had passed, however; therefore only 

 somatic cells from the growing root tips of 

 potted plants in the rosette stage have so far 

 been available for study; and it is the purpose 

 of this note, pending the completion of a more 

 general study of the (Enotheras, merely to call 

 attention to a most unexpected contrast found 

 in the number of chromosomes of 0. La- 



marchiana and one of its mutants, 0. gigas, 

 both pure bred. 



Because of the smallness of the chromatic 

 figures and the low percentage of figures 

 studied in which the chromosomes could be 

 counted with certainty, I do not at present 

 feel justified in stating the exact number in 

 either form ; but I can state unreservedly what 

 is of more interest, that in all the somatic 

 cells of 0. gigas arising from 0. Lamarckiana 

 in which the chromosomes could be counted 

 with precision, the number has hecome ap- 

 proximately dovMe that of the parental form, 

 0. Lamarckiana. This result was unexpected, 

 as a somewhat hasty survey of the tips of 



Oenothera. Lrommc ki'ano, , Oenoldevo. <j>^o.s . 



several other mutants previous to the study 

 of gigas had indicated a number closely ap- 

 proaching or identical with that of the pa- 

 rental form. Gates, in his " Preliminary 

 Note on Pollen Development in (Enothera lata 

 de Vries and its Hybrids," published in Sci- 

 ence, February 15, 1907, states that in a cross 

 resulting from the pollination of 0. lata by 

 0. Lamarckiana, " the sporophyte count for 

 the 0. Lamarckiana side of the cross is at 

 least twenty. The conclusion from this is 

 that pure 0. Lamarckiana itself must have 

 over twenty chromosomes." In his paper on 

 " Pollen Development in Hybrids of (Eno- 

 thera lata X 0. Lamarckiana, and its Eela- 

 tion to Mutation,'" he adds in a foot-note 

 on page 109 : " The inference that 0. La- 

 marckiana itself has the same number of chro- 

 mosomes as the dominant 0. Lamarckiana 

 hybrid is also apparently not borne out by the 

 facts." From my own observations on all 

 ^ Botanical Gazette, February, 1907. 



