30 



INTRODUCTION. 



an ovary is unilocular, bilocular, &c, according to the number of the cells. 

 When the margins of the carpel unite, there is a ridge or suture, called the 

 placenta ; this is central when the carpels are developed round a central 

 axis; parietal when, from the contraction of the dissepiments, projecting 

 from the inner surface of the ovary, but not dividing it into cells, the ovules 

 are placed near or on the walls of it. When there are several carpels united 

 in one mass, the pistil is said to be syncarpous ; where they are more or less 

 separated, it is called apocarpous. When an ovary forms no adhesion to the 

 sides of the calyx, its base and that of the stamens being inserted into the top 

 of the receptacle, it is said to be superior, and they are inferior or hypogy- 

 nous ; when it adheres to the side of the calyx, and the stamens and corolla 

 are inserted into the latter, or into a disk above the ovary, it is termed in- 

 ferior, and the other organs superior or epigynous. 



A flower being a transformed branch, each row or set of organs is a whorl 

 of leaves which has undergone a peculiar change, and hence there is a gradual 

 transition of ordinary leaves into those of the calyx, of the latter into petals 



and of these into stamens, and vice 

 Fig- 26. versa. In some plants the transition 



from the form of petal to that of stamen 

 is very marked ; this is the case in the 

 water lily, in which there are several 

 rows of petals, the outermost of which 

 are scarcely different from the calyx, 

 whilst the innermost are neither petals 

 nor stamens, but appear intermediate 

 between the two, — being petals bearing 

 Transformation of petals of Nymphsa into stamens, an imperfect anther; the next series 



are more reduced in size and have 

 perfect anthers, until finally perfect stamens make their appearance. In 

 what are called double flowers, the reverse takes place and the stamens are 

 converted into petals. A complete and regular flower should consist of four 

 whorls of an equal number of parts, alternate with each other. Thus if the 

 calyx have five sepals, the corolla should consist of five petals, alternate with 

 the sepals, the stamens be five, alternate with the petals, and the pistils five, 

 alternate with the stamens. This typical condition is, however, by no means 

 constant, being altered by a variety of causes ; as the production of one or more 

 additional whorls of some of the floral organs; by the union of the parts of 

 the same whorl; by a cohesion of their contiguous margins ; by a cohesion of 

 adjacent parts of different whorls ; by the suppression or abortion of some of 



Fig. 27. 



Fig. 28. 



Plan of flowers, a Cherry, ft Squill. 



Plans of flowers, a Primrose, b Samolus. 



the parts of a whorl, or of one or more of the whorls ; by an unequal dcvelope- 

 ment or unequal union of different parts of a whorl ; by changes in the form 



