146 



GROWTH AND WORK OF PLANTS 



species are on other individuals, the plants are dicecious (of two 

 households). When some of the flowers of a plant are imperfect 

 and others are perfect, they are said to be polygamous. 



230. Form of the flower. Flowers are regular, or irregular. 

 A regular flower is one in which all the parts of a set or series are 

 of the same size and shape. An irregular flower is one in which 

 some of the parts are of a different size or shape in some of the 

 sets (examples, flowers of the pea family, mint family, etc.). 



The corolla usually gives the characteristic form to the flower, 

 and the name is usually applied to it. Some of the different 

 forms are as follows: 



231. Regular flowers. Wheel-shaped or rotate when the 

 petals spread out at once like the spokes of a wheel, as in the 



Fig. 104. 



Several forms of flowers. Regular flowers, wh, wheel-shaped corolla; sa, salver-shaped; 

 tub, tubular-shaped. Irregular flowers, pa, butterfly or papilionaceous; per. personate or 

 masked flower; lab, gaping or ringent corolla. The two latter are called bilabiate flowers. 



potato, tomato, or bitter-sweet; salver-shaped when the petals 

 spread out at right angles from the end of a corolla tube, as in the 

 phlox; bell-shaped, or campanula^, as in the harebell or campan- 

 ula; funnel-shaped, as in the morning glory; tubular when the 

 petals spread but little or none from the end of the corolla tube, 

 as in the turnip flower, or in the disk flowers of composites. 



232. Irregular flowers. In the pea family the corolla is 

 butterfly-like or papilionaceous (fig. 120); the labiate corolla is 

 characteristic of the mint family where the corolla is unequally 

 divided into two lips. The ligulate or strap-shaped corolla is 

 characteristic of the dandelion, or of the ray flowers of the sun- 

 flower, etc. 



