ANGIOSPERMS. 



351 



we find structures of a quite different kind. The female flowers of lypha, for 

 example, and of some Cyperaceae are surrounded by hair-like bristles, and in the 

 Compositae there is a circle of hairs, the pappus, outside the corolla in place of a 

 calyx. The Gramineae have neither calyx nor corolla developed, the flowers being 

 enclosed in glumes which are forced apart from one another when the flowers unfold 

 by peculiar expanding bodies, the lodicules; these are small colourless scales of 

 delicate texture, and have been generally supposed to be a rudimentary and imperfect 

 perianth. It has already been mentioned that in Aconitum, Helleborus and other 

 plants, the leaves of the corolla are changed into peculiarly shaped nectaries. 



IV 



FIG. 272. Hippuris vulgaris. A a piece of an erect stem with the leaves of the whorl cut off, and flowers in their 

 axils. B transverse section of a flower above the ovary. C transverse section of the anther. / to IV longitudinal 

 sections through flowers in different stages of development, a anthers, f filament, n stigma, g style, p perianth, fk 

 inferior ovary, sk the pendulous anatropous ovule ; cp in B the carpel. 



If the perianth is composed of one or two whorls, the leaves of one whorl or of 

 both often appear to cohere or coalesce laterally, forming a shallower or deeper cup 

 or tube or similar figure, and the number of the coherent leaves of calyx or corolla is 

 usually shown by that of the marginal teeth. These coherent perianth-whorls are 

 due to the elevation, by intercalary growth in the form of an annular lamella, of the 

 common zone of insertion of the rudiments of the isolated leaf-structures formed on 

 the circumference of the torus ; the lamella assumes as it developes the structure of 

 the foliar whorl which it replaces. The coherent cup-shaped or tubular portion 

 therefore is not formed of parts originally free and subsequently united by their sides, 

 but it grows up from the first as a whole which may be said to be intercalated at the 

 base of the perianth-leaves ; the leaves which were at first free are the marginal teeth 

 of the common basal portion. Since a leaf of a calyx is called a sepal, and a leaf of 

 a corolla a petal, a calyx composed of coherent leaves is said to be gamosepalous, and 

 a corolla composed of coherent leaves gamopetalous ; if the leaVes of the perianth are 



