96 



THE STRUCTURE OF ECONOMIC PLANTS 



petals, the flower is regarded as isocarpic, and when the number of 



carpels is less than that of the other floral parts, it is said to be 



anisocarfic. 



In applying the facts of floral development and structure to 



phylogenetic interpretation, certain characteristics have come to 



be regarded as representing relatively high evolutionary position, 



while others seem to be indicative of primitive rank. In a general 



way, the following table indicates some of the high and low 



characters. 



TABLE I 



Relatively Low or Primitive Characters 



Spiral arrangement of floral parts 



Distinct parts 



Indefinite, usually large numbers of 



parts 

 Pentacyclic flowers 

 Hypogyny 

 Isocarpy 

 Actinomorphy 



Relatively High or Advanced Characters 



Cyclic arrangement of floral parts 

 Undiverged parts 

 Definite numbers of parts 



Tetracyclic flowers 

 Epigyny 

 Anisocarpy 

 Zygomorphy 



Vascular Anatomy of the Flower. — The divergence or non- 

 divergence of the floral parts is commonly associated with a diver- 

 gence or non-divergence of the vascular bundles which supply these 

 parts; and, in the last analysis, the interpretation of the floral 

 structures may rest upon their vascular anatomy. In simple types, 

 with a regular acropetal succession, the floral parts diverge one 

 above the other, in the same manner as foliage leaves, and each 

 floral structure has a distinct vascular bundle or bundles. In 

 types where there is a non-divergence of floral parts, there may be 

 an accompanying non-divergence of the vascular system; and, in 

 some instances, this reaches a point where it is not possible to dis- 

 tinguish between the stem tissue and the conjoint floral structures. 

 This situation occurs in many perigynous and epigynous flowers. 

 In the apple, for example, where the receptacle grows up around the 

 carpels, there is no delimitation between the carpels and the stem. 

 Vascular reduction of this type is generally associated with 

 advanced floral types, and non-divergence of the vascular system is 

 considered an advanced evolutionary character. 



In general, the primary vascular supply to a sepal consists of 

 the same number of bundles as supply the foliage leaf of the plant. 



