THE DICOTYLEDONES 1623 



cortex. Some species of Ranunculus are aquatic, in which case the leaves 

 may be heterophyllous; finely dissected leaves being developed below the 

 water. The petiole is usually broadened downwards into a sheath which 

 may be elongated into a pair of lateral, stipular lobes. 



The Ranunculaceae do not show any important anatomical peculiarities, 

 except in a few species. In Clematis the stem anatomy, particularly in the 

 climbing species, shows a separation of the secondary wood by wide medul- 

 lary rays similar to those in Aristolochia. Several circles of vascular bundles 

 occur in the stems of Cimicifuga and Thalictrum while medullary bundles 

 occur in Anemone japonica giving it the appearance of a Monocotyledon. 

 Hutchinson considers that there is a close relationship between this family 

 and the Alismaceae. 



The Ranunculaceae are classified as follows: 



I. Helleboroideae 



The ovules are numerous and the fruit is either a follicle, berry or 

 capsule. The flowers are usually in racemes, or in cymes or solitary. Nectaries 

 are present. Helleborus, Nigella, Eranthis, Actaea, Caltha, Trollius, Aqui- 

 legia, Delphinium, Aconitum. 



H. Paeonioideae 



The ovules are few in number and the fruit usually a follicle. The 

 flowers are usually solitary and nectaries are absent. Paeonia. 



HI. Anemonoideae 



There is a single ovule and the fruit is an achene. Anemone, Clematis, 

 Ranunculus, Thalictrum, Myosunis, Adonis. 



In the more primitive forms of the Helleboroideae, such as Helleborus 

 (Fig. 1479) and Caltha, ihe perianth is spiral and is continued from the spiral 

 arrangement of the foliage leaves. In Nigella the five perianth leaves are 

 generally followed by eight well-developed nectaries and an eight-rowed 

 superimposed androecium. The five to twelve carpels are often more or 

 less united. The zygomorphic Delphinium and Aconitum are based upon 

 a Nigella-Wke plan. The stamens and carpels are spirally arranged and show 

 none of the zygomorphic character of the sepals and petals. 



In Helleborus foetidus (Fig. 1480) the flowers are protogynous and insects 

 are attracted by the large sepals. When the sepals first open they remain 

 in a ring about i cm. across, through which the stigmas protrude. The 

 nectar is concealed in tubular nectaries, derived from petals, developed 

 between the stamens and the sepals, so that any large insect must brush 

 against the stigmas in its entry into the flower. Later when the carpels 

 have been fertilized the filaments of the stamens elongate in centripetal 

 order until the extrorsely dehiscing anthers completely fill the flower, 

 which opens to a diameter of about 2 cm. Insects now visiting the flower 

 will be liberally dusted with pollen before they can reach the nectar. 

 Damage to the flowers by rain is prevented by their pendulous position. 

 The visitors are chiefly bees. 



