128 PROTECTION OF POLLEN. 



The fact is also worthy of note that identical means of protection have not 

 always been evolved by members of the same family of plants. One has one 

 method of defence, another another. This diversity is exhibited particularly by 

 the various genera of Solanacese, and by the multifarious species of the genus 

 Campanula. In the Solanaceae we find the following variety of contrivances 

 according to the genus. The flowers of the Potato (Solanum tuberosum) fold 

 up in the afternoon and assume an inverted position owing to the curvature of 

 their stalks for the night, but only maintain it whilst the night lasts. The 

 next morning the flower-stalks straighten, and the flowers unfold again. The 

 Deadly Night-shade (Atropa Belladonna) has its flowers inverted during the whole 

 of the flowering season, and it is therefore not necessary for the corollas to open 

 and shut. The flowers of the Mandrake (Mandragora vernalis) remain erect, 

 but in the night and in rainy weather the tips of the upright corolla-lobes close 

 over the pollen-covered anthers inside. As regards the different Bell-flowers 

 (Campanula), those which have very long peduncles e.g. Campanula carpathica 

 and Campanula patula (cf. figs. 225 3 and 225 4 ) are only pendent in the night 

 and in bad weather; by day and in fine weather they are erect. They exhibit 

 pronounced periodic movements resulting in the curvature of their axes. In 

 other Bell-flowers with shorter stalks e.g. Campanula persicifolia, C. pusilla, 

 C. rotundifolia the buds nod before they open and continue in this position 

 throughout the time of flowering, whilst in those species wherein the flowers 

 are crowded together in heads and have very short stalks e.g. Campanula 

 Cervicaria, C. glomerata, C. spicata there is in general no curvature of the axes, 

 but the flowers remain upright and guard themselves against rain by means of an 

 inflection of the points of the corolla towards one another which closes the mouth of 

 the bell. Lastly, in the Venus' Looking-Glass, a plant nearly related to the Bell- 

 flowers, the flower closes by means of deep folds formed in the corolla. 



When contrivances have to be described which subserve several purposes 

 at the same time, it would lead to confusion to attempt to say everything that 

 there is to be said about them in one place. In such cases it is much more to 

 the purpose to keep one object alone in view even at the risk of appearing 

 one-sided to a hasty reader. This remark is particularly applicable to the 

 means of protection just described as being adopted by plants to preserve their 

 pollen from wet; for there is no question but that most of these contrivances 

 are capable of rendering other services to the plants in question besides the one 

 specified. In many cases the closing of petals effects not only the protection 

 of the pollen, but also its transference to neighbouring stigmas in the event 

 of a dearth of insect-visitors, as will be explained in a subsequent chapter. If 

 a flower-cup filled at the bottom with honey remained open to the rain the 

 honey would be immediately spoilt and would no longer act as an allurement 

 to insects. Hence we may infer that the shutting of the entrance to the 

 interior of the flower, the construction of the corolla-tube, and the change to 

 a nodding position in the case of melliferous flowers preserve not only the 



