DESCRIPTIVE TEEMS 



361 



parts of one or more sets of organs irregular in form, as in the 

 flowers of the pea, bean, and locust (Fig. 89). 



Floral plan. In a floral plan (Fig. 217>the parts of the flower 

 are represented in transverse section as though reduced to a 

 common plane. In dicotyledons the parts are usually in fours or 

 fives, while in monocotyledons they are on the plan of three. It 

 will be noticed also that the parts of each set of floral organs 

 alternate with those adjacent to them, like the leaves on a leafy 

 shoot. This alternate arrangement is another evidence that 

 flowers are modified shoots. 



Pollination features. The special structural and physiological 

 phenomena concerned with the pollination of flowers relate for 



b c 



FIG. 217. Floral diagrams 



a, lily family; b, heath family; c, madder family; d, composite family. The dot 



above b and d indicate the stem axis ; the sepals are represented with midribs ; the 



lighter stamens in b represent an alternate whorl of stamens. After Sachs 



the most part to devices for securing cross-pollination and 

 close-pollination. The more important of these structural and 

 physiological phenomena are the following: 



Anemophilous and entomophilous. The principal agents by 

 which flowers are close-pollinated or cross-pollinated are the wind 

 and insects. Flowers in which the pollen is carried to the stigma 

 by the wind, as in corn, poplar, and oaks, are said to be ane- 

 mophilous, or ^ wind-loving," while insect-pollinated flowers, like 

 the locust and bean, are said to be entomophilous, or " insect- 

 loving." Anemophilous flowers are usually characterized by in- 

 conspicuous color, abundance of light pollen, and lack of odor. 



Dichogamy. In many perfect flowers the stamens and stigma 

 mature at different dates in the same flower, a condition 

 defined by the term dichogamy (Fig. 218). If the stamens ripen 

 earlier than the stigmas in such flowers, the flowers are said to 



