Breeding experiments which show that hybridisation and mutation etc. 277 



ruhricalyx, i. e., plants having the fohage and habit of the 

 mutant lata combined with the red pigmentation of rubricaylx. 

 Doubtless all four of these plants contained 15 instead of 14 

 chromosomes (see p. 265), as was found to be the case with 

 one of the lata ruhricalyx plants examined. This furnishes 

 definite proof that the development of the lata (or scmilata) 

 foliage and habit results from the presence of the extra chromo- 

 some. This chromosome is a triplicate of two other chromo- 

 somes forming a pair, which are present in other races, and 

 the group of 15 evidently arises tlirough the union of germ 

 cells having respectively 8 and 7 chromosomes. 



I showed some years ago that in the reduction divisions 

 in pollen formation, nuclei containing 8 chromosomes are occa- 

 sionally formed through one chromosome passing to the wrong 

 pole of the heterotypic spindle. This completes the chain of 

 •evidence concerning the origin of the number 15, and inci- 

 dentally sliowi that the sporadic appearance of mutations, 

 from hybrids or any other source, is a process distinct from 

 hybrid combinations or blends. The cytological behaviour of 

 lata ruhricalyx will be described elsewhere. 



V. Bibliography. 



DE Vries, Hugo. 1901 — 3. Die Mutationstlieorie. Versuche und Beobachtungen über 

 die Entstehung von Arten im Pflanzenreich. Leipzig. 2 vols. 



— 1908. über die Zwilhngsbastarde von Oenotherci nauella. Ber. Deutsch. Bot. 

 Ges. 26a, pp. 667- — 676, 



— 191 1. Über doppeltreziproke Bastarde von Oenothera bieinii'. L. und Oenothera 

 muricata L. Biolog. Centralbl. 31. pp. 97 — 104. 



DoBELL, C. 1912 — 13. Some recent work on mutation in Microorganisms. Journ. 



Genetics 2, pp. 201 — 220, 325 — 350. 

 G.\TES, R. R. 190S. A study of reduction in Oenothera ridirinerui-i. Bot. Gazette 46. 



PP- 1—34- pis. 1—3- 



— 1909. xVn analytical key to some of the segregates of Oenothera. 20'!' Rept. 

 Mo. Bot. Garden, pp. 123 — 137. 



— 1910. The material basis of Mendelian phenomena. Amer. Nat. 44, pp. 203 

 — -13- 



— 1911a. Early historico-botanical records of the Oenotheras. Proc. Iowa Acad. 

 Science. 1910, pp. 85 — 124, pis. 6. 



— 1911b. Studies on the variability and heritability of pigmentation in Oenothera. 

 Zeitsch. f. ind. Abst. u. Vererbungslelire 4, pp. 337 — 372. pi. 6, figs. 5, tables 11. 



— 1912a. Parallel mutations in Oitiothera biennis. Nature 89, pp. 659— 660. 



