THE 1'LOWEE. 93 



in number. The multiplication in this case is often due to transverse chorisis, 

 the parts being superposed to each other. Each part so affected divides 

 in a direction parallel to its surfaces into two or more parts. If the 

 supernumerary part is an outgrowth from an already formed organ it is 

 said to be formed by enation. 



Pleiomery, or multiplication of the organs in particular whorls, 

 occurs in a number of flowers, and depends on different causes. 

 Sometimes the multiplication is effected by collateral chorisis, or divi- 

 sion at right angles to the surfaces, a pair of stamens, for example, 

 standing in place of one ; in other cases the organ is divided parallel 

 with the surfaces into an inner and outer part or into a fasciculus of 

 organs. The cases of collateral chorisis are explained by the circum- 

 stance that the staminal leaf, in these cases, as in an ordinary lobed 

 or compound stem-leaf, becomes subdivided and forms a lobed or 

 compound stamen. In some flowers (as in many Ericaceae) there are 

 ten stamens in one whorl, while the sepals, petals, and carpels are 

 pentamerous ; in these cases the five additional stamens are formed 

 subsequently to the others. This mode of multiplication of parts 

 is called interposition. 



Suppression, Abortion. In describing the phenomena of dimi- 

 nution of the number of circles or organs of flowers, it is convenient 

 to distinguish between suppression or total absence, and abortion or 

 partial absence, when the organs are represented by imperfect or 

 rudimentary structures. 



A complete flower possesses a calyx and a corolla ; the corolla, 

 and even the calyx also, are wanting in some flowers, which are 

 termed incomplete ; when the corolla alone is wanting, the flower 

 is apetalous:, the term naked is occasionally applied to flowers 

 without any floral envelopes. 



The term dichlamydeous, having calyx and corolla, monochlamydeous, 

 having calyx alone, and achlamydeous, destitute of floral envelopes, are 

 used by some systematic botanists in place of the above. These conditions 

 are not very secure bases for systematic divisions, since it is not uncommon 

 to find apetalous plants in Orders having ordinarily complete flowers, as 

 in the Oaryophyllaceae (Sayina, &c.) : the apetalous condition, however, 

 is constant in a large number of Orders, and familiar examples occur 

 in the Nettle family, the Chenopodiaceae, the Amaranths, &c. Achlamy- 

 deous flowers occur in the "Willows, Cattitriche, &c. Some flowers, then, 

 are incomplete by abortion, in which case they are degenerate conditions of 

 a more perfect type, or they are incomplete by suppression, when they 

 are typically of a relative low degree of organization. 



When essential organs (stamens and pistils) of both kinds are 

 present, the flower is called hermfiphrodite or bisexual (this condi- 

 tion is indicated by the sign ). It must be remembered, how- 



