APPENDIX A 513 



Corolla, petals 4, polypetalous, inferior, with a long basal claw. They are 

 cruciform, and alternate with the sepals. 



Androecium, stamens 6, free, hypogynous : two are short and lateral, 

 opposite the outer sepals ; four are longer in two pairs, opposite the inner 

 sepals. 



. Gynoecium, carpels 2, syncarpous, superior ; ovary bilocular, with many 

 ovules ; an ill-defined style, and a stigma with antero-posterior lobes. The 

 ovules are curved, and seeds ex-albuminous (Fig. 3, i. ii.). Fruit, a " siliqua " 

 which is a dry capsule, the lateral carpellary walls of which split from the 

 base upwards, leaving the two placentas as a frame with the transparent 

 septum stretched between them (Fig. 93). The septum is called " false " 



FIG. 419. 



Charlock (Brassica sinapis, Visiani). I. flower, with parts slightly displaced. 

 II. ripe and dehiscent fruit. III. floral diagram. 



because it is formed late, by ingrowths from the two opposite placentas, the 

 ovary being originally unilocular, as it is in the Poppies and in the Capers. 



Pollination. The flowers being grouped are conspicuous, and are visited 

 for their pollen, and for honey. The honey-secretion is by glands at the 

 insertion of the short lateral stamens. Insects passing from flower to flower 

 and inserting their proboscis, will probably effect intercrossing ; but self- 

 pollination is possible, and it is even provided for by the longer stamens 

 coming in contact with the stigma as the style elongates. It is not a highly 

 specialised type of flower and it is very constant in the Cruciferae, and may 

 be equally well studied in the Wallflower. The structure is probably di- 

 merous throughout, but with a fission of the median petals to form divergent 

 pairs, and of the median inner stamens to form the four longer. This is 

 expressed in the floral formula : S. 2+2, P. 2 x , A. 2 + 2 0> G. (2). 



The construction of the flower would then be theoretically as follows : 



Two antero-posterior sepals. 



Two lateral sepals. 



Two antero-posterior petals (by fission resulting in the four oblique petals). 



Two lateral stamens, short. 



B. B. 2 K 



