270 



TIIK FLOWER. 



the bud. This must almost necessarily occur wherever the parts" 

 are inserted at distinguishably different heights, and is the natural 

 result of a spiral arrangement. The name is most significant when 

 successive leaves are only partially covered by the preceding, as in 

 Fig. 207. Here they manifestly break joints, or are disposed like 

 tiles or shingles on a roof, as the term imbricated denotes. It is 

 therefore equivalent to the spiral arrangement : and, on the other 

 hand, we properly apply the term imbricated to any continuous 

 succession of such partly overlying members ; as when we say of 

 appressed and crowded leaves that they are imbricated on the stem, 

 or thus express the whole arrangement of the scales of a bud 

 (Fig. 153), or a bulb (Fig. 172), or of a catkin or cone (Fig. 209). 

 The alternation of the petals with the sepals, &c. necessarily 

 renders the floral envelopes likewise imbricated in the bud, taken as 

 a whole. But in proper aestivation, what we have to designate is 

 the arrangement of the parts of the same floral circle (say the five 

 sepals or the five petals) in respect to each oilier. 



494. Now when the sepals or 

 the petals are three in number, 

 and are regularly imbricated in 

 the bud, as in Fig. 437, the three 

 leaves are arranged just as in 

 three-ranked phyllotaxis (238, 

 Fig. 203) ; that is, with the first 

 lie second is covered by the first on 

 one side while it covers the third o:i the other. When they are five 

 (as in the calyx of Geranium, Fig. 439), they are disposed just as in 

 five-ranked or quincuncial phyllotaxis with the 

 axis shortened (240, Fig. 206) ; viz. two leaves 

 are exterior, two wholly interior, and one (the 

 third) with one edge covered by No. 1 on one 

 side while it covers No. 5 with its oilier edge. So 

 that this, the regular mode of imbrication when 

 the parts are in fives, is termed quincuncial aes- 

 tivation, or the parts are said to be quincuncially 



petal exterior to the others, th 



FIG 437. Diagram of a three-leaved (trimerous) calyx and corolla, both Imbricated in 

 aestivation. 



FIG 438 Diagram of tne estivation of three petals (or one circle of the petals) of Magno- 

 lia, similarly imbricated, but strongly enwrapping, each making nearly a circle 



FIG 439 Diagram of the imbricativo aestivation of the calyx and the convolutive aestiva- 

 tion of the corolla of Geranium ; the sepals numbered. 



