452 BOTANY 



in Dicotyledons, the number of carpels is smaller. The number of 

 members in the whorls of the perianth, andrcecium, and gynoecium is 

 indicated by the terms di, tri, tetra, pentamerous, etc. 



A TYPICAL ANGIOSPERMOUS FLOWER IS CONSTRUCTED OF FIVE 



ALTERNATING ISOMEROUS WHORLS, OF WHICH TWO BELONG TO THE 



PERIANTH, TWO TO THE ANDRCECIUM, AND ONE 



® TO THE GYNCECIUM. Flowers varying from this 



type have either continued in an undeveloped 

 stage, as those of the amentaceous plants, or, like 

 ? I ™ f(^f\ w 1 1 *^ e acv °li c flowers, they belong to a family which 

 il <JJ^S>/£? JF has been separated from the main line of descent, 

 ^V^xi ~S . or they have been subsequently modified from the 

 normal type in the course of phylogenetic evolu- 

 tion, like the flowers of the Orchidaceae and 

 Labiatae. 

 fig. 385. — Diagram of Only such variations from typical Angiosperm 



a pentacyclic flower n . • i • ,i • -i 



(Liiium) flowers are mentioned m this general summary as 



may have arisen by subsequent modification. To 

 avoid repetition the other special cases will be considered later in the 

 detailed description of the single flowers. 



A simple and not infrequent variation from the normal structure 

 is presented in flowers in which the stamens of the outer whorl are 

 opposite the petals, and those of the inner whorl opposite the sepals. 

 An andrcecium of this character is termed obdiplostemonous, as 

 distinct from the typical diplostemonous arrangement of the stamens. 



Another of the more common variations from the original type is 

 due to the multiplication of the whorls (pleiotaxy), often occurring 

 in the andrcecium (Rose), less frequently in the perianth (Berberis), very 

 rarely in the gyncecium (Punka Granatum). 



A variation of even more frequent occurrence results from the 

 diminution of the number of whorls (oligotaxy). This is often 

 shown in unisexual flowers, although by no means in all cases, as 

 the missing organs may be represented by reduced and function- 

 less parts, as in the similar case of the mammary glands of male 

 mammals. Thus in the female flowers the place of the stamens 

 is not uncommonly occupied by sterile staminodia. In hermaphrodite 

 flowers also a reduction of the number of whorls is often shown. The 

 occurrence of flowers with a simple perianth has already been mentioned ; 

 flowers with a simple andrcecium are still commoner. 



Such examples cannot, in all cases, be attributed to a reduction 

 from the normal pentacyclic type. On the contrary, they often 

 represent a primitive, more simple type (e.g. the flowers of the Nettle 

 and its allies). The absence of a whorl may only be referred to its 

 suppression, when such a conclusion is corroborated by other evidence, 

 such as, for example, may be derived from a comparison of allied 

 forms, as in the case of the Orchidaceae, in which the andrcecium is 



