528 BOTANY OF THE LIVING PLANT 



supported by the fact that in Samolus, Lysimachia, etc., five small staminodes 

 are present in the place where the missing stamens should be. The family 

 shows meristic variation, the whorls varying in number of parts from four to 

 nine. Trientalis and Lysimachia are specially variable. 



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 

 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. 



{h) TETRACYCLICAE. 

 ORDER: PERSONATAE. 



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 usuall^^ large. 



Family: Solanaceae. Examples: Nightshade, Potato. 



(36) The Deadly Nightshade {Atropa Belladonna, L.) is a perennial herb 

 of shrubby habit, with entire leaves having a clammy glandular surface. It 

 bears its flowers solitary in the axils of leafy bracts. The whole inflorescence, 

 which is cymose, starts with a single terminal flower, below which strong 

 branches .develop, the ultimate branchings of which are complicated by 

 adhesions. The flower consists of : 



Calyx, sepals 5, gamosepalous, inferior ; the odd sepal is posterior. 



Corolla, petals 5, gamopetalous, inferior, alternating with the sepals ; very 

 sUghtly zygomorphic. 



Androecium, stamens 5, hypogynous, epipetalous ; filaments curved. 



Gynoecium, carpels 2, syncarpous, superior, placed obliquely to the median 

 plane ; style elongated, stigma capitate, ovary bilocular, ovules numerous, 

 placentation axile. A honey-disc surrounds the base of the ovary. 



Fruit, a large black berry, surrounded by the persistent green calyx. Seeds 

 albuminous, embryo curved. 



Pollination. The colour and honey-secretion offer attractions to bees, 

 especially humble-bees, while the gamopetalous corolla and the stiff hairs 

 at the base of the filaments tend to exclude small crawling insects. The 

 stigma and anthers mature almost simultaneously. The stigma projects 



