MOBPHOLOGY OF EEPRODUCTIVE ORGANS 151 



when the number of petals is much increased, in which there is 

 a gradual transition from the sepals to the petals, so that it is 

 difficult or almost impossible to say, in many oases, where the 

 calyx ends and the corolla begins. The White Water-lily {jig. 

 276) affords a familiar and good illustration of this. In some 

 plants, again, the green colour disappears, and the calyx becomes 

 coloured with the same tints as the corolla, or with some other 

 bright hues. In such cases it is said to be petaloid, and the 

 chief distinctive character between it and the corolla is then 

 afforded by its position on the outside of the latter organ. The 

 Fuchsia, Indian Cress, Columbine, Larkspur, and Monkshood may 



Fie. 285. 



Fig. 28S. 



Fuj, 285. Vertical section of the flower of the Rose, r, r. Concave tbalamus, 

 upon which are placed several carpels, o, o, each of which is furnished with 



a style and stigma, s. e, e. Stamens. Fitj. 286. Flower of iloukshood 



(Aconitum ^''ape2lvs), with an irregular polysepalous calyx. The upper 

 gepal is hooded or helmet-shaped. 



be mentioned as affording familiar examples of a petaloid calyx 

 amongst Dicotyledons. In Monocotyledons generally, as in the 

 Lily, Iris, Tulip, Crocus, and Squill, the two floral envelopes are 

 usually coloured, although sometimes green, and in other re- 

 spects resemble each other so closely, that the collective name 

 of perianth is used to indicate the two whorls taken together. 

 When there is but one whorl of floral envelopes, as in the Goose- 

 foot {fig. 255), it is customary to call this the calyx, whether it is 

 coloured or green. 



In their structure, venation, and characters generally, the 

 sepals resemble the foliage leaves. They exhibit various cha- 

 racters as regards their figure, margins, apex, &c., although 

 they are by no means liable to such numerous variations in 

 these particulars as the blades of foliage leaves exhibit. The 



