iVlORPHOLOGY OF ANGIOSPERMS. 137 



are irregular. Regular Hovvers are also spoken of as actino- 

 MORPiiic or RADIAL, aiicl irregular flowers as zygomorphic. The 

 latter are also spoken of as dorsiventral. Dorsiventral flowers 

 either arise as such, as in some of the Leguminosse (Fig. SS), 

 or they may arise as radial flowers and become dorsiventral 

 during the course of development, as in willow herb (Epilobium). 



In some flowers the floral envelopes are wanting, and the 

 flowers are said to be naked, as in the willows and grasses. 



Anthotaxy. The study of the arrangement of flowers on 

 the stem is known as anthotaxy. The flowering axis may bear 

 only a single terminal flower, as in Tulipa ; or the flowers may 

 occur singly in the axils of the leaves, as in Viola canadensis. 

 When, on the other hand, the flowers are borne upon a branch 

 shoot, the internodes of which are more or less condensed, and 

 the leaves smaller and of a more simple structure than the 

 foliaceous leaves, the whole shoot is known as an inflores- 

 cence, and the leaves are called i'.racts. The flower thus repre- 

 sents a single unbranched shoot, while the inflorescence repre- 

 sents a branched or ramified shoot. 



The so-called bracts besides being generally smaller than the 

 leaves proper are mostly sessile ; they may, however, be green, or 

 membranaceous, or they may exhibit a bright coloration, as in 

 Monarda. 



The stalk of the individual flower is called a pedicel, and 

 may be naked, or bear one or two small bracts, which are 

 called FORE-LEAVKS or prophylea. In the monocotyledons there 

 is usually only one fore-leaf, which turns its back to the mother- 

 axis and is frequently two-nerved and two-keeled. In the 

 dicotyledons there are generally two fore-leaves, which are placed 

 to the right and left of the flower, as in the violets. 



The position of the floral leaves ( the sepals, the petals and 

 those of the perianth) depends upon the arrangement of the 

 fore-leaves, so that in most of the monocotyledons, where there 

 is one mediane prophyllon, the first leaf of the perianth is placed 

 on the front, while the two succeeding leaves of the perianth 

 occupy a position of 120 from this (Fig. 124). When, on the 

 other hand, as in the dicotyledons with pentamerous flowers 

 two fore-leaves are developed, the first floral leaf (sepal) is 



