FLOWERS AND THEIR WORK 



35 



A flower of the sedum from 

 above; A, anther; C, carpel; 

 F, lament ; P, petal ; S, sepal. 

 Notice how the parts come 

 out in circles or whorls. 



latter being in the center of the flower. The structures with the 

 knobbed ends are called stamens. In a single stamen the boxlike 

 part at the end is the anther; the stalk is called the filament. The 

 anther is in reality a hollow box which produces a large number of 

 little grains called pollen. It is neces- 

 sary for the reproduction of new plants 

 that the pollen get out of the anther. 

 Each carpel or pistil is composed of a 

 rather stout base called the ovary, and 

 a more or less lengthened portion rising 

 from the ovary called the style. The 

 upper end of the style, which in some 

 cases is somewhat broadened, is called 

 the stigma. The stigmatic surface 

 usually secretes a sweet fluid in which 

 grains of pollen from flowers of the 

 same kind can grow. 



Pollen. — Pollen grains of various 

 flowers, when seen under the micro- 

 scope, differ greatly in form and appearance. Some are rela- 

 tively large, some small, some rough, others smooth, some spherical, 

 and others angular. They all agree, however, in having a thick 



wall, with a thin membrane under 

 it, the whole inclosing a mass of 

 protoplasm. At an early stage the 

 pollen grain contains but a single 

 cell. When we see it, however, we 

 can distinguish two nuclei in the 

 protoplasm. Hence we know that 

 at least two cells exist there. 



Growth of Pollen Grains. — Under 

 certain conditions a pollen grain will 

 burst open and grow. This growth 

 can be artificially produced in the 

 laboratory by sprinkling pollen from well-opened flowers of 

 sweet pea or nasturtium on a solution of 15 parts of sugar to 

 100 of water. Left for a few hours in a warm and moist place 

 and then examined under the microscope, the grains of pollen will 



A pollen grain highly magnified. 

 It contains two nuclei (n, n') at 

 the stage here represented. 



