ii62 A TEXTBOOK OF THEORETICAL BOTANY 



and it is not necessary to assume that it is always of the same character. It 

 usually arises on clawed petals at the junction of the two parts, or at the 

 mouth of the floral tube in sympetalous corollas, which is morphologically 

 the same situation. It has been interpreted as representing petal ligules, 

 petal stipules, staminal stipules, simple emergences, foliar modifications of 

 the upturned basal lobes of sterile anthers, or invaginations of the petal 

 tissues. The last condition is obvious in Symphytum, w^here the teeth of the 

 paracorolla are really hollow pockets, and the same explanation holds for 

 Lychnis, where however the hollow structure can only be made out in 

 sections. Although the corona, as a united structure, is best known in the 



Fig. 1 133. — Passifloro coerulea. Longi- 

 tudinal section of flower showing 

 the ring of blue-and-white striped 

 effigurations inside the corolla. 

 {After Engler-Prantl.) 



above-mentioned family, the Amaryllidaceae, a paracorolla of separate 

 segments is prominent in several dicotyledonous families, e.g., Thymelaea- 

 ceae, Gentianaceae, and Passifloraceae. In Passiflora (Fig. 1133), indeed, 

 the long, blue-and-white striped filaments of the paracorolla quite outshine 

 the corolla itself in beauty. Here they have plainly no connection with the 

 stamens and would appear to be outgrowths from the petal bases, but in 

 Gentiana two different structures are apparently involved. In G. amarella 

 the paracorolla filaments are like those of Passifhra, petal outgrowths, but 

 in G. verna and some other species, staminal stipules have become united 

 together outside the stamens filaments and have also become more or less 

 united to the corolla, giving the same appearance of a paracorolla as in 

 G. amarella. 



In Amaryllidaceae also, both types of structure are represented. The 

 Pancratiae have a corona which is definitely staminal in origin and mostly 

 united to the androecium (Fig. 1 134), but in Narcissus (Fig. 1 135) the corona 

 is explained by Arber as due to ligular outgrowths of the petals, which are 

 reversed in orientation, as shown by their vascular bundles, so that the two 



