340 



HUTCHINSON'S POPULAR BOTANY 



FIG. 415. HONESTY 

 (Lunaria). 



Section of flower showing saccatt 

 calyx. 



In contrast to the Wallflower, take a Pansy 

 (Viola"). A Pansy is a good example of an irre:/"f"r 

 flower. By cutting through the centre perpen- 

 dicularly we get two similar halves, but in no 

 other way can the flower be divided symrne trie- 

 ally. Flowers exhibiting this kind of bilateral 

 symmetry are known as monosymmetrical or zyyo- 

 morphic (Greek zeugnumi, I join, and morphe, a 

 shape). Flowers the petals of which are placed 

 like the spokes of a wheel, and which may there- 

 fore be divided vertically into similar halves 

 through two or more planes, are termed actinomor- 

 phic (Greek aktin. a spurious form of aktis. a ray, 

 and morphe]. All regular flowers are actinomor- 

 phic : most irregular flowers are zygomorphic. 

 Some flowers cannot be symmetrically divided in 

 any plane they are asymmetric. 

 There is a curious fact about the Pans}'. What appears to be the lower- 

 most petal is really the upper, for the flower has been reversed. It has been 

 thought that the purpose of the curve in the flower-stalk is to strengthen 

 the flower and thus to enable it to sustain the weight of insects. When 

 a honey-bee visits a Pansy, it almost always turns round on alighting, and 

 sucks with its head downwards, and the flower is bent down by the insect's 

 weight a circumstance which indirectly bears out this idea. Notice the 

 streaks of colour on the petals, all leading towards the centre of the flower. 

 They are honey-guides for the insect visitors pathfinders, as some have 

 named them. There will be more to say about 

 these pathfinders on a future occasion, but allusion 

 is made to them here by way of emphasizing the 

 contrast which the petals of this flower present to 

 those of another common flower, the White Cam- 

 pion i Lychnis vespertina, fig. 416). The pure white 

 corolla of this species of Campion has no guiding 

 marks : in this case they would be of no service, 

 for the flower expands in the evening, and insects 

 are attracted to it by its whiteness. There are 

 five petals, attached by claws to the base of a 

 tubular calyx, and these are the characteristic fea- 

 tures of a caryophyllaceous corolla. The Maiden 

 Pink (Dianthus deltoides). Carnation (D. caryophyl- 

 lus} : and Catchfly (Silene) exhibit the same features. 

 The rosaceous corolla consists of five petals, too, 

 but the}- are without claws : the Buttercup (Ra- 

 nunculus, fig. 419) is a good example. 



FIG. 416. WHITE CAMPIOX 



(Lychnis vespertina), 



With styles exserted. 



