• ORGANS OF REPRODUCTION. i>21 



afford in enabling ns to ascertain the relative succession and 

 position of the parts of the flower on the axis. The term an- 

 thesis is sometimes nsed to indicate the period at -which the 

 flower- bud opens. 



Besides the definite and constant relations which the parts of 

 the flower have to each other in the flower-bud, they also have a 

 determinate and constant relation in the same plant to the axis 

 upon which they are placed. In describing these positions we 

 use the terms anterior or inferior, superior or posterior, and lateral. 

 Thus, we call that organ posterior or superior, which is turned 

 towards the axis, and that next the bract from the axil of 

 which it arises, inferior or anterior. When there are four or- 

 gans in a whorl, one will be superior, one inferior, and two 

 lateral, as in the calyx of Cruciferous Plants (fg. 421). If there 

 are five we have two arrangements. Thus, in the calyx of the 

 Pea tribe of plants (Leguminoscp) two sepals are superior, two 

 lateral, and one iiferior ; while in the corolla, in consequence of 

 the law of alternation in the parts of the floAver to be hereafter de- 

 scribed, one petal is superior, two inferior, and two lateral {Jig. 

 463). In plants of the Rose tribe {Rosace(B),vfe have a precisely 

 reverse position exhibited by the two outer floral whorls ; thus, 

 here we have two sepals inferior, two lateral, and one superior; 

 while in the corolla there are two petals superior, two lateral, 

 and one inferior {fig. 462). From these relations of position 

 being constant in the plants of Rosace^e and Leguminosse, we 

 have here a constant character by which those orders may be 

 distinguished. 



The same definite relation with respect to the axis also holds 

 good in many cases in the staminal and pistilline whorls, by 

 which important distinctive characters are frequently obtained, 

 as will be seen afterwards when treating of Systematic Botany. 



Section 3. — The Floral Envelopes. 

 1. THE calyx. 



"We have already stated that the calyx is the outermost 

 envelope of the flower, and that it is composed of one or more 

 leafy organs called sepals. These sepals are usually green like 

 true leaves, by which character, as well as by their position, 

 and more dehcate texture, they may in most cases be dis- 

 tinguished from the petals. There are numerous instances, 

 however, in which there is a gradual transition from the sepals to 

 the petals, (especially when there is more than one whorl of these 

 organs,) so that it is difficult or almost impossible, to say where 

 the calyx ends and the corolla begins. The White Water-Lily 

 {Nt/mphcea alba) {fig. 438), affords a familiar and good illustra- 

 tion of this. In some plants again, the green colour disappears, 

 and the calyx becomes coloured with the same tints as the 



