146 



MANUAL OF BOTANY 



outgrowth or placenta, and at the base of the latter there are two 

 ovules. Similar cones occur among the Cj'cads, some of which 

 have both miorosporophylls and megasporophylls so arranged. 

 Spiral phyllotaxis also occurs in the Angiosperms in certain 

 families where the normal phyllotaxis of the flower is whorled, 

 though it is less common than the other cases of interference 

 with typical symmetry. There are two degrees in which it 

 exists, a. The whole of the floral leaves may be arranged 

 spirally, as in the Water-Uly {NymphcBa) {fig. 276). Here the 

 members of the separate whorls show gradual transition from 

 one form, to the next. The outer leaves are green and sepa- 

 loid ; as we pass inwards their green hue is gradually replaced 



Fig. 276. 



Fiq. 276. Mower of the White Water-lily {Ntjirtplma alba) reduced in size. 

 After Jussieu. c, c, c, c. The sepals. /i,^,2j,/i. Petals. '.Stamens. Tlie 

 pacts ou the right show the gradual transition from the sepals, c, to the 

 petals, p, and from these organs to the stamens, e. The stamens from 

 1 to 5 arL- gradually more distinctive. 



by white, till they are evident petals ; there is a similar tran- 

 sition from petals to stamens, the leaves becoming narrower 

 and indications of anthers appearing at their summits, till the 

 definite staminal form is reached. Such flowers are known as 

 acyclic, h. The perianth may be in whorls and the sporophylls 

 arranged spirally. This is the case in the Buttercup, where 

 there are two series of spirals, the androeoium and gyncecium. 

 They do not show a transition to each other as in the former 

 case. The flower of the Buttercup is termed hemicyclic. Some- 

 times the whorls of the perianth are not true ones, but result 

 from a condensed spiral. This may be seen in such corollas as 

 have a quincuncial sestivation (see page 210). 



8. Metamorphosis of Parts of the Flower. — A modification 



