270 



THE I'LOWEU. 



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 otlier 

 hand, we jiroperly apply the term imbricated to any continuous 

 succession of such partly overlying members ; as when A\e 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 other. 



494. Now Avhen the sepals or 

 the petals are three in number, 

 // // \\\\ //'/ ' ^^>S ^"^ ^^*® regulai'ly imbricated in 



■f f rl (Hi M\ the bud, as in Fig. 437, the three 



leaves are arranged just as in 



three-ranked pliyllotaxis (238, 



437 438 Fig, 203) ; that is, with the first 



petal exterior to the others, the second is covered by the first on 



one side while it covers the third on 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 other edge. So \ 



that this, the regular mode of imbrication Avhen 



the parts are in fives, is termed quincuncial ajs- 



tivation, or the parts are said to be quincuncially 



439 



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

 seBtivation. 



FIG 438. Diagram of the a?stiTation 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 imbricative Kstivation of the calyx and the conyolutlTe sestiTa- 

 tion of the corolla of Geranium ; the sepals numbered. 



I 



