APPENDIX A 



641 



Pollination. Compare first the " thrum-eyed " type of flower. The parts 

 are numerically the same as in the " pin-eyed " ; but the style carries the 

 stigma only half-way up the corolla-tube, corresponding in level to the stamens 

 of the " pin-eyed." The stamens are inserted at the throat of the corolla, 

 corresponding in level to the stigma of the " pin-eyed." The effect of this 

 " dimorphism " is to increase the probability of intercrossing as a consequence 



Fig. 492. 



Primula vulgaris. I. short-styled type of flower (thrum-eyed) in section. II. long- 

 styled type (pin-eyed). III. pollen of short-styled. IV. of long-styled types. 

 V. stigmatic papillae of short-styled. VI. of long-styled type. VII. floral diagram. 



of repeated visits from bees to the two types of flower, which are borne on 

 different plants. The sticky pollen deposited on the proboscis of the bee 

 from the " pin-eyed " type will correspond in level to the stigma of the " thrum- 

 eyed," and the pollen of the latter to the stigma of the former. These are 

 what have been called " legitimate " crosses, and they have been shown to be 

 more prolific than the " illegitimate ' crosses, between parts of unequal 

 length. But self-pollination is not precluded. The gamopetalous corolla is 

 effective in excluding smaller insects, while bees are attracted by honey, 

 colour, and scent. 



(d) TETRACYCLICAE. 

 ORDER : PERSON ATAE. 



This Order includes a large number of showy plants of temperate and 

 tropical climates, with tetracyclic, gamopetalous flowers, having the general 

 formula S. 5, P. (5), A. 5, G. (2). The ovary is superior, and bilocular, and the 

 number of ovules borne on the axile placenta is usually large. 



