CHAP. IIL LINUM GRANDIFLORUM. 81 



CHAPTER III. 



HETEROSTYLED DIMORPHIC PLANTS continued. 



Linnm grandiflorum, long-styled form utterly sterile with own-form 

 pollen Linum peienne, torsion of the pistils in the long-styled 

 form alone Homostyled species of Linum Pulmonaria officinalis, 

 singular difference in self-fertility between the English and German 

 long-styled plants Pulmonaria angustifolia shown to be a distinct 

 species, long-styled form completely self-sterile Polygonum fago- 

 pyrum Various other heterostyled genera Rubiacese Mitchella 

 repens, fertility of the flowers in pairs Houstonia Faramea, 

 remarkable difference in the pollen-grains of the two forms ; tor- 

 sion of the stamens in the short-styled form alone ; development 

 not as yet perfect The heterustyled structure in the several 

 Rubiaceous genera not due to descent in common. 



IT has long been known* that several species of 

 Linum present two forms, and having observed this 

 fact in L. flavum more than thirty years ago, I was 

 led, after ascertaining the nature of heterostylism in 

 Primula, to examine the first species of Linum which 

 I met with, namely, the beautiful L. grandiflorum. 

 This plant exists under two forms, occurring in about 

 equal numbers, which differ little in structure, but 

 greatly in function. The foliage, corolla, stamens, and 

 pollen-grains (the latter examined both distended with 

 water and dry) are alike in the two forms (Fig. 4). 

 The difference is confined to the pistil ; in the short- 

 styled form the styles and the stigmas are only about 

 half the length of those in the long-styled. A more 



* Treviranus haa shown that original paper, 'Bot. Zcitimg,' 

 this is thccaae in his review of my 1863, p. 189. 



