184 PHYLLOTAXY, OR LEAF-ARRANGEMENT. 



their phyllotaxy, and partly of the way in which they comport 

 when their margins meet in growth. Those leaves which are 

 within, or of higher insertion on the axis, will almost necessarily 

 be enclosed or overlapped : those which are members strictly 

 of the same whorl or cycle may fail to come into contact, or 

 may meet without overlapping at the contiguous margins or 

 apex ; yet they may be overlapped, since they may have grown 

 unequally or some a little earlier than their fellows. Conse- 

 quently, no perfectly clear line can be drawn in the flower between 

 cycles and spirals except by their mode of succession. More- 

 over, aestivation strictly so called should be concerned only 

 with the disposition among themselves of the several members 

 of one whorl, or of one complete spiral. So the alternation of 

 contiguous whorls, as of the three inner with the three outer 

 flower-leaves of a Lily or a Tulip (the alternative aestivation of 

 DeCandolle) , is a matter of phyllotaxy, not of aestivation. The 

 latter is properly concerned only with the relations of each three 

 leaves to each other. 1 



253. The proper aestivations may be classified into those in 

 which the parts do not overlap, and those in which they do. Of 



the first, there are two kinds, the open (cest. 



aperta) and the valvate, both characterized and 



named by Brown. 2 Of the second, there is 

 i^]| \\ one leading kind, the imbricate (adopted by 

 ' j) Brown from Linnaeus) , with subordinate modi- 

 <v ^<^ fications. 8 Accordingly, the aestivation is 



said to be 



255 254. Open or Indeterminate (cest. aperta), 



when the parts do not come into contact in the bud, so as to 



1 The same applies to the two sets of sepals and of petals in Barberry, in 

 Menispermum, and of the petals in Poppy, &c. (359). 



, 2 Linnaeus, indeed, has, " ^Estivatio valvata, si petala se expansura instar 

 glumae graminis ponuntur," the name, but not the thing: the glumes of 

 grasses are not valvate in the botanical sense. So the term as to its proper 

 use may be said to originate with R. Brown. 



8 For a brief discussion of " ^Estivation and its Terminology," see Amer. 

 Jour. Sci. ser. 3, x. 339, 1875. 



As to names, it is perhaps more correct to say of the (estivation that it is 

 imbricative, convolutive, valvular, &c. (cest. imbricativa, convolutiva, valvaris, &c.), 

 but of the leaves or pieces, that they are imbricate, convolute, valvate, &c., in 

 aestivation ; but such precision of form will seldom be attended to in botan- 

 ical descriptions. 



FIG. 255. Diagrammatic cross section of an unopened flower of Linden : its outer 

 circle of floral leaves (sepals) valvate In the bud; the Inner (petals) between convolute 

 and imbricate. 



