THE EMERGENCE OF THE FLORAL WHORLS. 187 



Exactly the same procedure occurs in Sparmamiia 

 and Philadelphus, which are tetramerous, as compared with 

 Tilia and Ueutzia respectively, which are pentamerous (see 

 p. 18). 



The next point to be noticed is the alteration in the 

 order of emergence which takes place in irregular flowers. 

 The rule seems to be that those parts of the flowers which 

 assume a greater prominence in the mature state, or have 

 some special function beyond the rest, emerge and develop 

 before the others. Thus in Leguminosce and Lahiatce, where 

 there is a prominent "landing-place " for insects, the petals 

 issue successively in an antero-posterior order. The carina 

 of papilionaceous flowers composed of two petals appears 

 first, then the al^ together, and finally the vexillum. In 

 Reseda, the sepals, petals, and stamens issue in a postero- 

 anterior manner ; but while the sepals finally attain to much 

 the same dimensions, the petals remain more or less atrophied 

 as they emerge towards the anterior side. Then the stamens 

 appear in the same order upon a cellular ring, which, later 

 on, grows out into the unilateral disk between the petals and 

 stamens. 



In a few regular flowers the simultaneity is also wanting . 

 thus in Adoxa the sepals of the tetramerous terminal flower 

 emerge in pairs, and the four petals simultaneously ; but in 

 the lateral flowers the posterior sepals issue before the 

 anterior; and of the five petals the posterior one emerges 

 first, the two lateral secondly, and the two anterior ones last 

 of all. These modifications are continued in the order of 

 flowering. Thus the terminal flower expands first, and " all 

 at once." Of the lower lateral flowers the two upper 

 posterior sepals open out first, then the posterior stamens 

 mature and shed their pollen. The anthers dehisce in suc- 

 cession from the lateral stamens, and lastly from the anterior 



