HYBRID OF DIGITALIS. 365 



segregation of factors, backcrosses with plants which are the 

 immediate descendants of the parents which produced the hybrid 

 itself should afford evidence as valuable as offspring obtained by 

 self-fertilisalion of the hybrid. The problem is, do the factors 

 governing like characters in the two species really mingle and 

 become alike in the hybrid, or do they remain different, so that 

 either the gloxinia flora (P) or the lutea (Y) type is transmitted 1 



The gametic nature of the hybrid, according to Mendelian 

 theory, may be represented as PY, of gloxinia flora as PP, and of 

 lutea as YY. The question is, when the backcross, say, hybrid x 

 gloxiniozflora, is made, do the factors P and Y in the hybrid 

 remain distinct, or have they influenced each other, so that we 

 have actually to do with a new factor resulting from their mutual 

 influence ? In the case of all the measurable characters dealt with 

 it will be seen that the inheritance appears to have the nature of 

 a blend. 



On the crossing of the purple foxglove (Q) gloxiniozflora 

 (PP), with the vellow species (cf) lutea (YY), the characters in 

 the hybrid are often not intermediate in nature. 



Leaves. — Ln the hybrid the ratio of breadth to length of the 

 leaf is nearer to that of gloxiniozflora than to that of lutea: number 

 of stomates nearer to lutea; hairiness nearer to lutea: rate of 

 desiccation of plucked leaves nearer to lutea; size of epidermal 

 cells, intermediate; length of stomates, intermediate; indenta- 

 tions, distinct from either (PI. IV, fig. 2). 



Flowers. — Absolute length and breadth of flower and ratio, 

 nearer to gloxiniozflora; degree of spotting, nearer to lutea 

 (PI. IV, fig. 2); intensity of purple colouration, intermediate. 



Thus out of 12 characters the hybrids were approximately 

 intermediate in 3, nearer one parent or the other in 8, and dif- 

 ferent from either parent in 1. 



Resembling one parent more strongly than the other in any 

 given character is a common feature of interspecific hybrids, and 

 it would be referred to as dominance by the Mendelians, and to 

 prepotency by those who favour the view that a blend of homo- 

 logous factors has occurred. 



8. Comparison of Backcrosses with Hybrids and Parent 



Species. 



Since only one hybrid plant was appreciably fertile, we are 

 practically confined to the offspring arising from crossing this 

 hybrid plant with both parent species. The only other backcross 

 secured consisted of a single plant resulting from the pollination 

 of a gloxiniozflora plant with the pollen of a second hybrid plant. 

 This particular backcross has not yet flowered. It has the 

 peculiarity of the leaves being very strongly coloured with purple. 

 The colouration is due to the epidermal cells containing a bright 

 purple sap. The edges of the leaves of normal gloxiniai flora are 

 occasionally tinged with purple, but nothing approaching the con- 

 dition of this backcross has ever been seen in either parent species. 



