66 EEV. G. HENSLOW HOMOLOGY AND 



This occurs in " double flowers." Since, however, what are popu- 

 larly called double flowers may have very different origins, it will 

 be as well to consider them as a separate subject. 



It often happens that a flower, though apparently quite as 

 "double'' as some other, Avhich may be entirely so, is not really 

 like the latter ; hence the following varieties may be distinguished 

 and which will explain such differences as occm\ 



1. Cai'pels only petaloid. Anemone nemorosa, Viola, and Gen- 

 tiana Amarella.'^' 



2. Stamens multipKed and more or less petaloid, with the pistil 

 normal or more or less unchanged. Tacsonia,] white hyacinth, 

 Chinese primrose. 



3. Do. with the pistil foliaceous of two leafy carpels. The 

 double cherry. 



4. Do. with the pistil replaced by a tuft of green leaves. 

 The purple hyacinth. 



5. Petals multiplied with no change in stamens and pistil. 

 Double stocks. 



6. Do. with entire loss of stamens and pistils. Wallflowers, 

 Ranunculus, rose, and many of the garden " double flowers." 



7. Hose-in-hose fonns : — (1.) Calyx and corolla repeated one 

 within the other. Hdiantheinum vidf/are. (2.) Calyx petaloid. 

 Primula, 31imulus, Azalea, Campamda persicifolia. (3.) A cata- 

 corolla. Campanula. (4.) Inner perianth-whorl resembling the 

 outer. Iris, Orchis. 



It must not be supposed that the above cases never vary. It is 

 more than probable that they do. But as far as observations go, 

 they seem to be tulerably true for the different methods given. 



The conversion of stamens or carpels to petals may be in- 

 completely effected, so that, just as a distinction between virescence 

 and foliation may be made, when they become green ; so petaloid or 

 truly petaline may be recognised as corresponding degrees of 

 metamorphosis, as in the following cases. 



1. Connective only petaloid, e.g. Primula, Fuchsia, etc. 



2. Filament ,, (normal) e.g. Nymphcea, Atragene. 



,, ,, (abnormal) e.g. Hibiscus Rosa-sinensis. 



Double composite flowers are due, — ( 1 ) to the conversion of the disk 

 pentamerous tubular florets into ligulate trimerous florets, by the 

 suppi'ession of two petals, and all the stamens : while the arms of 

 the style undergo a reduction in size. Or they may be caused 

 (2) by elongation of the tube with the five-toothed border more or 

 less suppressed. This furnishes the ' quilled ' form. Or (3) the 

 border may be also abnormally enlarged, hence arise the ' dragon ' 

 forms of Chrysanthemum. 



In the double Poinsettia, which is remarkable for its brilliant 

 foliage, the "doubling" merely consists in the increase of the 

 number of coloured leaves obtained in some cultivated varieties.;]: 



* 'Gardeners' Chronicle,' 1843, p. 628. 

 t 'Gardeners' Chronicle,' 1875, p. 167. 

 X For further details on double flowers see ' Teratology,' Appendix, p. 491. 



