47-2 JOURNAL OF THE ROYAL H0RTICTTLTT7RAL SOCIETY. 



evidently be somewhat different from those obtaining in the ordinary 

 case of simple Mendelian inheritance, and for the present a statement 

 of the facts is all that is possible. 



The second class of double mentioned above, in which doubling is due 

 to an actual multiplication of whorls, is well seen in Lobelia (fig. 170). 

 Here we have a less commonly occurring condition, viz., doubling in 

 a flower with irregular (isobilateral) symmetry. In the single flower 

 there are four whorls altogether, one each of calyx, corolla, stamens, 

 and pistil, the corolla being bilabiate. In the double-flowered indi- 

 viduals the number of perianth whorls may be greatly increased, e.g. 

 in a good specimen of the strain * Kathleen Mallard ' six or more extra 

 whorls of corolla may be seen. Some plants, on the other hand, only 

 develop one additional whorl, while others again exhibit intermediate 

 grades. But though the number of whorls thus varies considerably in 

 different plants, it is usually constant for the individual. The mem- 

 bers of each whorl regularly alternate with those of the next, though 

 in very double specimens the innermost ones are sometimes incom- 

 plete, the suppression of some members in these cases possibly being a 

 mechanical necessity due to lack of space.* Here again, as in the 

 Columbine, the regular alternate arrangement of the several whorls, 

 and the fact that one sees repeated in turn in the inner whorls the 

 symmetry and colour pattern of the outer ones points tO' true multipli- 

 cation as the cause of the augmentation in number. When only one 

 extra whorl is present either as calyx or corolla (making three altogether) 

 the reproductive organs remain normal and produce good ovules and 

 pollen (fig. 2, B and e). This is occasionally found to be the case also 

 when the number of perianth whorls is increased to four, but more 

 often the stamens then become completely transformed so that the 

 ovary alone remains functional (fig. 2, c and f). When a larger number 

 of whorls occur both stamens and carpels are converted into petaloid 

 structures, and neither ovules nor pollen are produced. Such plants 

 being completely sterile can only be propagated by vegetative methods, 

 whereas the lower grades can be bred from, like the singles (fig. 170, d 

 and g). 



We may now consider some examples of the more frequently 

 occurring types of double where, instea'd of true multiplication, we 

 find splitting in varying degree either in the petals or more commonly 

 in the stamens which have become petaloid. In such cases a regular 

 arrangement of these supernumerary structures is not usually dis- 

 cernible, though some exceptions occur, as e.^. in the Chinese 

 Primrose {Primula sinensis), where these additional structures are few 

 in number. The ordinary type of double of the present day shows 

 within the corolla proper a second row of petaloid structures standing 

 opposite to those of the outer row and having their surfaces reversed, 

 the more brightly coloured facing towards the outside, the paler 

 towards the inside of the flower. Following upon these are the five 



* According to Goebel these last irregularly arranged members probably 



represent modified carpels {loc. eft. p. 254). 



