THE DICOTYLEDONES 1831 



This series is interesting because, as the size of the flowers diminishes 

 and they become less Hkely to receive insect visits, provision is made that, in 

 the event of cross-polhnation faihng, self-polhnation becomes inevitable. 



Before leaving the pollination mechanisms in this family we must refer 

 to the peculiar condition found in Erodium cicutarium. It has been clearly 

 shown in this species that two distinct kinds of flowers occur, which are 

 associated with two methods of pollination. The first is termed var. 

 genuimim and in this the petals are uniformly red and of equal size, though 

 the upper ones are sometimes rather shorter and darker in tint than the 

 lower. The nectaries are developed as in Geranium. Although ten stamens 

 are formed, only the five opposite the petals develop anthers. Of these, 

 three are longer and while the anthers dehisce they lie close to the stigmatic 

 branches. Later the two others dehisce similarly so that automatic self- 

 pollination is inevitable. Moreover this process takes place early in the 

 morning, within an hour of the opening of the flowers, and by midday the 

 petals have been shed. Since the variety is self-fertile good viable seeds 

 are formed. 



The second variety, which is termed pimpinelltfolium, is entomophilous. 

 The flowers are larger and the two upper petals are small and broad as 

 compared with the three lower ones, which are elongated to provide a 

 platform for alighting insects. At first the centre of the flower is closed by 

 the stamens, but the nectar is obtainable between the stamens and the 

 two upper petals. Then the three upper and, later, the two lower 

 anthers dehisce, while the stamens curve further and further outwards. 

 At this stage the style is quite short and undeveloped. The day after the 

 anthers have dehisced the styles grow up and expand. Thus, normally, 

 self-pollination is prevented, though occasionally, if cross-pollination 

 is not successful, the stamens may bend inwards making self-pollination 

 possible. 



The Geraniums of our gardens have been artificially produced as hybrids 

 of the genus Pelargonhim. The so-called zonal pelargoniums have been 

 produced by crossing P. zonale with P. inquinans, while many of the larger- 

 flowered varieties have originated from crosses with P. grandifloriim. Some 

 possess specially scented leaves, as for example P. crispiim which is lemon- 

 scented, P. tomentosum which is peppermint-scented and P. fragans which 

 has the scent of nutmeg. P. endlicherianum is the only species which is 

 hardy in Britain. It is a bushy perennial, growing about 2 ft. high with rose- 

 red flowers. 



We may refer briefly here to the small but important order the Rutales, 

 which contains the families Rutaceae and Meliaceae. The members of this 

 order are trees, shrubs or climbers, but rarely herbs. The leaves are dotted 

 with glands and may be either simple or compound. 



The Rutaceae are a small family with about 100 genera and 800 species, 

 which are widely distributed in warm temperate regions. The flowers are 

 regular or occasionally slightly zygomorphic and there are usually either 



