420 



DICOTYLEDONE&. 



FIG. 437. Diagram of 



Tropceolum, : sp, spur. 



sperm is wanting. 



climb by their sensitive petioles. The flowers are situated 

 singly in the axils of the foliage-leaves on long stalks, arid are 

 zygmnorpliic, the receptacle under the posterior sepal being pro- 

 longed into a spur ; there are also differences between the posterior 

 and anterior petals, the 2 posterior petals situated on the border 

 of the spur being perigynous, and the edge 

 of the anterior petals adjoining the claw 

 fringed. After the 5 sepals (which are 

 more or less coloured) and the 5 petals, 

 follow 8 stamens (as the 2 median ones are 

 suppressed, one from each whorl) and a 

 gynceceum formed of 3 carpels ; in each of 

 the 3 loculi of the 3-grooved ovary is 1 

 ovule. The fruit is a schizocarp and divides 

 into 3 1-seeded, drupe-like fruitlets, which 

 do not (as in the Geraniacese) leave any 

 pronounced column between them. Endo- 

 The cotyledons are thick and sometimes 

 slightly coalescent. Tubers often occur. 



Tropceolum. About 40 species ; all from America. 



POLLINATION. The spur is the receptacle for the nectar; the flowers are 

 protandrous ; the anthers open first, and one by one take up a position in front 

 of the entrance to the ppur, resuming their original position when the pollen is 

 shed ; the stigma finally takes their place after the filaments have bent back- 

 wards. These plants have an acrid taste (hence the name " Nasturtium," 

 "Indian Cress"), on which account the flower-buds and young fruits of 2'. 

 majus are used as capers. Some species are ornamental plants. 



Order 5. Balsaminaceae. Herbaceous, chiefly annual plants 

 with juicy, brittle stems, so transparent that the vascular bundles 

 may be distinctly seen. The leaves are simple, usually scattered, 

 penninerved and dentate; stipules are wanting, but sometimes 

 large glands are present in their place at the base of the petioles. 

 The flowers are strongly zygomorphic; of their five 5-merous 

 whorls the petal-stamens are suppressed (S5, P5, A5 + 0, Go); 

 the sepals are coloured, the 2 anterior ones (Fig. 438 j, j) are 

 very small or entirely suppressed, the posterior one is very large 

 and elongated into a spur, and the 2 lateral ones pushed forward ; 

 sometimes the weight of the spur turns the flower completely 

 sound, so that the posterior leaves assume an anterior posi- 

 tion - apparently only 3 petals, since the lateral and the pos- 

 terior petals become united in pairs, and the anterior is larger 



