llß S. IKENO : 



aiid Pdnnett liave foimd in F^ ex HL x hl (j)iu-ple flower aud long poUeu by 

 red and roiand) tlie linkage of the series 7:1:1:7 between B aud L, wldlst 

 in furtlier generations of the same cross that of the series 15 : 1 : 1 : 15 has 

 been obseiTed ;' also in the same plant and in the same kind of the ci'oss 

 PuNNETT has obseiTed sometimes the 7:1:1:7 linkage, aud sometimes the 

 10 : 1 : 1 : 10 oue." Again, in the progeny of one of liis ]Maize hybrids 

 (endosperm homy-waxy, coloured-wliite) Kemptox has generally detected the 

 linkage belonging to the series 3:1:1: 3, -svhilst iu the progeny deriyed 

 from the same pai-ents he could find that of the series 3:2:2: 3, though 

 exceptionally.' Piecently experiments to modify artificially the amount of 

 linkage in Drosopldla by the influence of yarying temperatm-es haye been 

 earned on mth success by Plough.* The yariation of the linkage ratio in 

 the cross imder discussion is thus no imi^recedented fact ; whether it is due to a 

 certain change in the internal mechanism, or to the influence of the euyironment, 

 or to cei-taiu other reasons is howeyer yet unsettled, and -\\iU lie the interesting 

 subject of futm-e studies. Furthermore, though in om- present case we haye 

 seen the complete hukage of jB aud B iu F. and its change into a partial 

 iu F-i, it is yery doubtful whether such would be always the case. It seems 

 to me very probable that there might be several modifications. Thus, for 

 instance, the absolute Unkage of R aud B seen iu F., might remain as such 

 in i^ ; on the contrary, theh- partial linkage or even their fiee combination 

 might occiu already iu F,, etc., etc. StiU fiuther, some other important 

 questions will await the answer. Thus the fact should be determined whether 

 the ratio of liukage ^\■ill remain constant iu all cases. Also it v.W\ bo 

 necessary to investigate the fact whether or not this ratio -nill be ecpial on 

 the male as A\eU as the female side of one aud the same plant. As one of 

 the exti-eme cases of the inequality of the liukage ratio on the two sides we 

 might have, for iustauce, that where the linkage is complete on one side and 

 partial on the other ; nor would it he not impossible that on the oue side we 



eiepei-imeridelle Vererbungslehre, 3. u. 4. Aufl., 1019, j). 172 flF. 



' Jieport to the Evohdion Committee R. S., Eeport t, ViOO, p. 11 ff. 



'■^ Jmtrn. of Genetics, Vol. 3, 1913, pp. 78-79 ; ako il)i<l., A'ol. 6, 1917, p. 187. 



3 U. S. DejKirtmeni of Agric, lixtU. 754, 1919, p. 78 ff. 



* Jonm. of experim^tmi Zooi, Vol. 21, 1917, pp. 147-209. 



