FLOEAL ENVELOPES— CALYX. 195 



with fig. 290 that the part marked 2 has, by a slight change in posi- 

 tion, become overlapped by 4. In flowers, such as those of the Pea 

 (p. 205, fig. 316), one of the 

 parts, the vexillum, is often 

 large and folded over the 

 others, giving rise to vexillary 

 aestivation, or the carina may 

 perform a similar oflBce, and 

 then the aestivation is carinal. ^'s- ^so. Kg. 291. Fig. 292. 



The several verticils often diifer in their mode of sestivation. 

 Thus, in Malvaceae, the corolla is contortive and the calyx valvate, or 

 reduplicate (fig. 288) ; in St. Johns-wort the calyx is imbricate, and 

 the corolla contortive. In Convolvulacese, while the corolla is twisted, 

 and has its parts arranged in a circle, the calyx is imbricate and 

 exhibits a spiral arrangement (fig. 290). In Guazuma (fig. 285), the 

 calyx is valvate, and the corolla induplicate. The circular sestivation is 

 generally associated with a regular calyx and corolla ; while the spiral 

 sestivations are connected with irregular as well as regular forms. 



The different parts of the flower, besides having a certain position 

 as regards each other, bear also definite relations to the floral axis 

 whence they arise. An individual part of a flower may be turned to 

 one or other side of the axis, to the right or to the left. This law 

 often holds good with whole groups of plants, 'and a means is thus 

 given of characterising them. , If a whorl of the flower consists of 

 four} parts, that which is turned towards the floral axis is called 

 superior or posterior, that next the bract whence the pedicel arises is 

 inferior or anterior, while the other two are lateral. If, again, there 

 are five parts of the whorl, then two may be inferior, two lateral, and 

 one superior, as in the corolla of the Pea tribe ; or one may be in- 

 ferior and two superior, as in the corolla of the Kose tribe. In plants 

 having blossoms like the Pea, the vexillum, or odd petal, is the 

 superior part ; whilst in the calyx the odd part, by the law of alter- 

 nation, is inferior. Sometimes the twisting of a part makes a change 

 in the f)osition of other parts, as in orchids, where the twisting of 

 the ovary changes the position of the labellum. 



Uxternal Floral Whorls, or Floral Envelopes. 



Calyx. — The calyx is the external envelope of the flower, and 

 consists of verticillate leaves, called sepals, foliola or phylla (folium, 



Fig. 290. Transverse section of calyx in flower-bud of Convolvulus sepium. Calyx con- 

 sists of five sepals corresponding to the numbers in the figure, and the dotted lines indicate 

 the direction of the spiral according to which they are arranged. Fig. 291. Transverse 

 section of the bud of Magnolia grandiflora, showing the convolute sestivation of the three 

 outer leaflets (calyx). Fig. 292. Arrangement of the parts of the calyx in the flower of 

 Frogsmouth (Antim-liiMum majus). The arrangement diflfers from that in fig. 290, on ac- 

 count of a Blight twisting and overlapping of the parts. 



