224 



PLANT STRUCTURES 



yledons the number five prevails, but often four appears, 

 forming pentamerous or tetramerous flowers (Fig. 199). 

 This does not mean that there are necessarily just three, 

 four, or five of each organ in the flower, for there may be 

 two or more cycles of some one organ. For example, in the 

 common lily there are six floral leaves in two sets, six sta- 

 mens in two sets, and three carpels (Fig. 204). 



In the cyclic flowers it is also to be noted that each set 

 alternates with the next set outside (Fig. 204). The petals 



are not directly opposite the se- 

 pals, but are opposite the spaces 

 between sepals ; the stamens in 

 turn alternate with the petals ; if 

 there is a second set of stamens, 

 it alternates with the outer set, 

 and so on. If two adjacent sets 

 are found opposing one another, 

 it is usually due to the fact that 

 a set between has disappeared. 

 For example, if a set of stamens 

 is opposite the set of petals, either 

 an outer stamen set or an inner 

 petal set has disappeared. 



This line of evolution, there- 

 fore, extends from flowers whose 

 parts are spirally arranged upon 

 an elongated receptacle and in- 

 definite in number, to those whose parts are in cycles and 

 definite in number. 



122. Hypogynous to epigynous flowers. In the simpler 

 flowers the sepals, petals, and stamens arise from beneath 

 the ovary (Figs. 197, 202, 205, 1). As in such cases the 

 ovary or ovaries may be seen distinctly above the origin 

 (insertion) of the other parts, such a flower is often said to 

 have a "superior ovary." The more usual term, however, 

 is hypogynous, meaning in effect "under the ovary," refer- 



FIG. 204. Diagram of such a 

 flower as the lily/showing re- 

 lation of parts : uppermost 

 organ is the bract in the axil 

 of which the flower occurs ; 

 black dot below indicates po- 

 sition of stem ; floral parts in 

 threes and in five alternating 

 cycles (two stamen scts\ being 

 a trimerous, pentacyclic flow- 

 er. After SCHIMPER. 



