MORPHOLOGY OF EBPEODUCTIVE OEGANS 211 



It frequently happens that the calyx and corolla exhibit dif- 

 ferent kinds of sestivation. Thus, in Ouazuma ulmifoUa the 

 calyx is valvaie, and the corolla induplicaie. In Malvaoeous 

 plants the calyx is valvate or shows some form of circular 

 aestivation ; and the corolla is twisted. Again, in the Corn 

 Cockle (Giihago segetum), the species of St. John's Wort 

 {Hypericum), the Geranium, and many other- plants, the calyx 

 is quincuncial or imbricate ; and the corolla twisted. 



The kinds of fsstivation above described are always constant 

 in the same individual, and frequently throtighout entire genera, 

 and even natural orders ; hence they are of great importance in 

 Systematic Botany. 



The term a/nthesis is sometimes used to indicate the period 

 at which the flower-bud opens. 



Besides the definite and constant relations which the parts 

 of the floral envelopes have to one another in the flower -bud, 

 they have also a definite and constant relation in the same plant 

 to the axis upon which they are placed. In describing these 

 positions we use the terms anterior, posterior, and lateral. 

 Thus, we call that part posterior which is turned towards the 

 axis ; and that next the bract from the axil of which the flower 

 arises, anterior. When there are fovir leaves in a whorl, one 

 will be anterior, one posterior, and two lateral, as in the sepals 

 of the Wallflower. If there are five we have two arrange- 

 ments. In the calyx of the order Leguminosse, two sepals a,re 

 posterior, two lateral, and one anterior ; while in the corolla 

 one petal is posterior, two anterior, and two lateral {figs. 303 

 and 464). In plants of the order Eosacese we have a 

 precisely reverse position exhibited by the parts of the two 

 floral envelopes ; here we have two sepals anterior, two 

 lateral, and one posterior ; while in the corolla there are two 

 ■petals posterior, two lateral, and one anterior. 



The same definite relation with respect to the axis also holds 

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

 which important distinctive characters are frequently obtained. 

 In floral diagrams it is usual to indicate the position of the axis 

 upon which the flower is placed by a dot placed over the 

 posterior part of the diagram. 



The Ovule. 



As the anther has been shown to be comparable to a sorus 

 consisting of four or more sporangia, so we may regard each 



