STUDIES ON THE GENETICS OF FLOWER-COLOURS, ETC. 127 



actual unmljcr of the two kiuds of segi'cgates does not verj- woll iigiec witli 

 the expected (expactatiou on 3:1 basis, 93-75±4-8 : 31-2ü±4-8). How the 

 magenta of snch composition has arisen fi'om the white cannot yet be determined, 

 and though its origin might be perhaps infeiTed this is merely a matter of 

 c^injactm-e, and it wonld not be worth while to state here such an inference. 



II. Reversion in ike Somatic Cell. — To this class belongs No. 11 in 

 Table YIII. Supiwse that the i-evci-se mutation has occmTed in a certain 

 somatic cell of the composition CCt'i'bb, at least one cell-gjnaration before 

 the reducing division, and supposa further that this cell has got the composi- 

 tion CCIirhh in consequence of this process. From th-? hitter coll the male 

 and the female gametes Clib and CHt \\\\\ be derived after one or more 

 cell-generations acojrding to diftei'eut cases. The fertilisation between them 

 will give rise to zygotes consisting of 1 CCRBhb, 2 CCTtt'bb and 1 CC- 

 rrbb; the pixKluction of 20 reds and 5 oranges in No. 11 may be due 

 to such a process (expected 1875±2 and G'25±2). - 



III. The mutations described in I and 11 are, as already stated, tha 

 i-evei-se ones, i.e. those from recessive to dominant condition. The mutations in 

 the opposite sense, i.e. those fi-om dominant to recessive condition (so-called 

 " loss-mutation ") have been also obsei*ved sometimes, though not fi-equently, 

 to which might belong Nos. 23 and 29 in Table YIII. In No. 29 one 

 orange which shoidd lae theoretically homozygous, i.e. CCrrbb, has produced 

 1 magenta, 118 oranges, and 58 whites. According to oiu- hypothesis a 

 certain somatic cell having the genotj-pic composition CCrrbb lias undergone 

 a " loss-mutation," and changed into Ccrrbh ; the gametes Crb and crb 

 are derived fi'om it after a number of cell-generations, and their fi'ee assort- 

 ment has given rise to oranges and whites in the approximate ratio 3 : 1 (119 

 oranges: 58 wliites, theoretically 132-75±5-8 : 44-25±5'8, if we M-ill count 1 

 magenta as orange); 1 magenta was produced at the same time, perhajis 

 Vecause 1 gamete CRB has aiisen by reversion of h into JS. Thus the 

 whole process in No. 29 consists in loss-mutation and revei-sion combined. 



No. 23 (magenta) was found to segi-egate in F., into magentas and reds, 

 whence we might at once be led to the assumption tliat that magenta parent 

 should have the composition CCRBBb (75 magentas; 42 reds, expected 

 87-75±-l-7 : 29-25±4-7). Since however this pai-ent has been originally derived 



