280 THE FLOWER. 



when successive leaves are only partially covered by the preced- 

 ing, as in Fig. 174-176 ; here they manifestly break joints, or are 

 disposed like tiles or shingles on a roof, as the term imbricated de- 

 notes. It is therefore equivalent to the spiral arrangement, which 

 word is sometimes substituted for it in eestivation : and, on the 

 other hand, we properly apply the term imbricated to any contin- 

 uous 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. 127), or a bulb (Fig. 141), or of a catkin or cone 

 (Fig. 175). The alternation of the petals with the sepals, &c., 

 necessarily makes 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. 



493. Now where the calyx or the corolla exhibits the character 

 of a complete cycle (439) or of a part of a cycle (442) of leaves 

 with the internodes undeveloped, that is, where we may perceive 

 on close inspection that the several members are inserted on the 

 receptacle at unequal heights, this will be manifested in the bud 

 by the relative position of these members : the lower or outer must 

 overlie or inclose the upper or inner. This is just the case in reg- 

 ular imbricative aestivation ; where, of five sepals, for example (as 

 in the diagrams, Fig. 300, 281), two will be wholly exterior in the 

 bud, two wholly interior, and one intermediate, namely, covered at 

 one edge by one of the exterior, while its other edge overlies that of 

 one of the inner sepals ; which, on comparison with Fig. 172, 

 173, will be found to correspond exactly with the f or quincuncial 

 arrangement of leaves as presented on a similar ground-plan. 

 Leaves No. 1 and No. 2 are external ; No. 3 is internal in respect 

 to these, but external in respect to No. 4, which is two fifths of the 

 circumference distant, and more manifestly to No. 5, which, being 

 separated by an interval of two fifths from the preceding, com- 

 pletes the cycle, and is overlapped by No. 3. In this, the normal 

 and the most common arrangement in. the 5-merous flower, the 

 parts are said to be spirally, or (with more definiteness as to the 

 numerical kind of spire) quincuncially imbricated in aestivation. 



494. We have here the advantage of being able to number the 

 successive sepals, or petals, since the third leaf is not only recog- 

 nizable by its intermediate position, but also indicates the direction 

 in which the spiral turns, as is shown in Fig. 173. 



