MODIFICATIONS OF THE FLORAL ORGANS. 



Fig. 74. Fig. 75, 



175 



flower in which the parts are arranged in fives is said to be 

 pentamerous, (rthts five, jts'poj a part.) 



In monocotyledons, on the contrary, we observe more fre- 

 quently the number three or one of its multiples, or the flower 

 is trimerous, (ftpsi$ three, ^'po* a part.) Fig. 75 is a good illus- 

 tration. It is a diagram of the flower of the snow-flake, 

 (Leucojum), a monocotyledonous plant, having three sepals, 

 three petals, six stamens in two alternating rows, and three 

 carpels. This flower is symmetrical, complete, regular, and 

 trimerous. 



The number of extra verticils which are developed is some- 

 times very considerable, as in the Cactus and white water-lily, 

 (Nymphaea.) In such circumstances it is easy to perceive 

 that the disposition by verticils is only apparent and that the 

 floral leaves are arranged in a spiral about the axis of growth. 

 The spiral law not only produces the orderly distribution of 

 the leaves about the stem, but ensures the same symmetry in 

 the floral organs, producing that regular, alternation of the 

 parts of each verticil, and in these plants a very perceptible 

 spiral arrangement of them. 



The parts of the floral organs may have been increased by 



