12 



BRITISH FLOWERING PLANTS 



their scent at particular hours ; thus, Hesperis matron- 

 alis and Lychnis vespertina smell in the evening, and 

 Hahenaria hifolia is particularly sweet at night. 



Besides the means of attracting welcome guests, 

 many plants have adopted various devices for barring 

 access to their stores of honey of insects whose visits 

 would be of no use in transferring pollen. For instance, 



in the case of bee flowers, 

 small flying insects are 

 kept from the nectar by 

 barriers of stifli' hairs which 

 they are not strong 

 enough to pass — e.g. Tro- 

 pseolum. Creeping insects, 

 as ants, are frequently 

 kept back by sticky hairs 

 on the stem or flower-stalk 

 — as in many Saxifrages. 

 A large proportion of 

 dicotyledonous flowers 

 have five sepals and five 

 petals. Why is this ? 

 It is probably to be ex- 

 plained by the phyllo- 

 taxy, or arrangement of 

 the leaves on the stalk. 

 The petals, as Goethe 

 seems first to have sug- 

 gested, are modified 

 leaves. Now if we ex- 

 amine a Rose shoot (Fig. 

 4) we shall find that the 

 leaves are arranged in a 

 spiral round the stem in 

 such a manner that with 

 whatever leaf we start the sixth comes directly over it, 

 the seventh over the second, and so on. In fact, the 

 leaves form whorls of five, one over the other. This is 

 still more evident in those species which have a five- 



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Fig. 4.— Shoot of Rose. 



