FLORAL ENVELOPES. CALYX. 171 



contrasted with. fig. 266, that the part marked 2, by a slight change 

 in position, has become overlapped by 4. In flowers, such as those 

 of the Pea (^[ 379, fig. 292), one of the parts, the vexillum, is often 

 large and folded over the others, giving rise to vexittary aestivation, 

 or the carina may perform a similar part, and then the aestivation 

 is carinal. 



356. The different verticils often differ in their mode of aestivation. 

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

 reduplicate (fig. 264). In Convolvulaceae, while the corolla is twisted, 

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

 exhibits a spiral arrangement (fig. 266). In Guazuma (fig. 261), the 

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

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

 spiral aestivations are connected with irregular as well as regular forms. 



357. The different parts of the flower, besides having a certain 

 position as regards each other, bear also definite relations with respect 

 to the floral axis whence they arise. An individual part of a flower 

 may be turned to the one or the other side of the axis, to the right or 

 to the left, in its normal state, and the same will be the case with the 

 corresponding parts of the other flowers. This law often holds good 

 with whole groups of plants, and a means is thus given of character- 

 izing 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 are inferior, two lateral, and one superior. 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 alternation, is inferior. 

 Sometimes the twisting of parts makes an apparent change in their 

 position. 



External Floral Whorls, or Floral Envelopes. 



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

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

 (jt/AXov, a leaf). These calycine leaves are sometimes separate from each 

 other, at other times they are united to a greater or less extent ; in 

 the former case, the calyx is polysepalous or polyphyllous (TTOX<>?, many), 

 in the latter gamosepalous or gamophyllous, monosepalous or monophyl- 

 lous (-/dpo;, union, or pt,c,vog, one). The divisions of the calyx present 

 usually all the characters of leaves, and in some cases of monstrosity 

 they are converted into the ordinary leaves of the plant. This is 

 frequently seen in the Rose (fig. 226 c), Paeony, &c. Their structure 

 consists of cellular tissue or parenchyma, traversed by vascular bundles, 

 in the form of ribs and veins, containing spiral vessels, which can be 



