SYMMETEY OF THE FLOWER. 



93 



Arrests and suppressions are due to failures of development, and affect more than 

 all other causes the symmetry of the flower. Arrest is the condition of an organ 

 the growth of which has stopped, so that it is reduced to a sort of stump, sometimes 

 glandular ; suppression implies that an organ has never even been developed. The 

 outer whorls are more seldom arrested or suppressed than the androecium and espe- 

 cially the pistil, which occupies but a narrow area of the receptacle. The suppression 

 or arrest of one or more pieces of a whorl affects the symmetry of number, position 

 and form. For example, Berberis, whose calyx, corolla and andrcecium are in threes 

 or multiples of three, has for pistil a single carpel ; the Pink (fig. 488), whose other 

 whorls are quinary, has but two carpels ; the Heartsease three 

 (fig. 489) ; in the Bitter Vetch (fig. 490) and other Papilion- 

 acece, the two first whorls are quinary, the third decennary, 



488. Pink. 

 Diagram. 



492. S'jrophularia. 

 Diagram. 



491. Snapdragon. 

 Diagram. 



whilst the pistil is mono-carpellary ; it is the same with the pistil of the Plum and 

 Peach. The Snapdragon (fig. 491), of which the calyx and corolla are quinary, has 

 (owing to arrest) four stamens, and two carpels due to suppression. 



In Scrophularia, with the same arrangement, the fifth stamen is represented by 

 a petaloid scale (fig. 492). The Periwinkle and other Apocynece, as well as many 

 monopetalous families, have five sepals, five petals, five slamens, and two carpels ; 

 Polygala (fig. 493) has five sepals, three petals (sometimes five, alternating with the 

 sepals), eight half anthers (equivalent to four stamens), and two carpels. Umbel- 

 lifercB (fig. 494) have five sepals, five petals, five stamens and two carpels. The 

 Corn/lower, Dandelion, Chrysanthemum and other Composites have quinary corollas 

 and androecia and a single carpel ; in most, the calyx degenerates into a pappus, 

 though in some (Asteriscus, Hymenoxys) it presents five scales. In most Cucurbitacece 

 (Melon, Pumpkin, Cucumber] the calyx and corolla are quinary and the stamens are 

 reduced to two and a half. 

 In apetalous, monoecious, 

 and dkecious flowers, an 

 entire whorl is suppressed 

 or arrested (Lychnis, Sagina, 

 Chenopodium, fig. 189) ; some- 

 times several whorls are 

 absent, as in the Nettle and 

 Mulberry (fig. 495), which 

 present only a calyx with an andrcecium, or a pistil. Sometimes several whorls are 

 suppressed, together with one or more pieces of the remaining whorl ; the male flower 



493. Polygala. 

 Diagram. 



494. Coriander. 

 Diagram. 



495. Mulberry. 

 g flower (mag.). 





