SECT. II 



PHANEKOGAMIA 



501 



produced than by "illegitimate" fertilisation, and in some cases {Linum perenne, 



Fig. 456. — Primuht. si)iensis : two heterostyled flowers from different plants. L, Long-styled, 

 K, short-styled flowers ; G, style ; S, anthers ; P, pollen -grains, and N, stiginatic papillae of 

 the long-styled form ; p and n, pollen-grains and stigniatic papillae of the short-styled form. 

 (P, N,p, «, X 110.) 



Fagopijrwm esculentum) legitimate fertilisation alone is productive. Legitimate 



fertilisation is rendered more certain by the fact that insects in visiting the 



flowers touch correspondingly placed 



sexual organs with the same portions 



of their body. The flowers of Primroses 



have styles of two different lengths 



(dimouphic heterostyly) ; the same 



peculiarity is exhibited hj Pulmonaria, 



Hottonia,, Fagopyrum, Linum. There 



are also flowers with trimorphic 



HETEROSTYLY {Lythrum salicaria, and 



some species of Oxalis) in which there 



are two circles of stamens and three 



variations in the height of the stigmas 



and anthers. 



In a great number of flowei'S self- 

 pollination is made mechanically im- 

 possible, as their own pollen is pre- A — 

 vented by the respective positions of 

 the sexual organs from coming in con- 

 tact with the stigma (Hercogamy). 

 In the Iris, for example, the anthers 

 are sheltered under the branched petal- 

 oid style. The conveyance of pollen Fig. 457. -Flowers of AristolocUa dematitis cut 



from the older to the younger flowers 



is efl'ected in Arislo/ochia by small 



insects. The flowers at tirst stand 



upright with a widely-opened mouth 



(Fig. 457 /), and in this condition 



the insects can easily push past the downwardly directed hairs clothing the 



tubular portion of the corolla and reach the dilated portion below. Their 



through longitudinally. /, Young flower in which 

 the stigma (X) is receptive and the stamens (S) 

 have not yet opened ; //, Older flower with the 

 stamens opened, the stigma withered, and the 

 hairs on the corolla dried up. (>: 2.) 



