244 



General Biology 



The purpose of a flower is the production of seed. The ripened 

 carpel, with its contained seed, is known as a fruit. (Fig. 150.) 



The buttercup (Fig. 151) will serve as an excellent example of the 

 flowering plants. Here we have many carpels (simple pistils) each 

 made up of an ovary (the simple closed cavity below) which gradually 

 tapers to a soft terminal stigma. The carpels are flat and open when 

 the plant is young, but they gradually have their margins curve upward 

 and close. During the time the carpel is closing, an ovule grows out 

 from the base and becomes enclosed by the carpel walls. 



There are several rows of stamens encircling the pistils. Each 

 stamen or microsporophyl bears four elongated, parallel, sporangia con- 

 taining pollen or microspores. The stalk of the stamen is called the 

 filament, while the four pollen-sacs (sporangia) are known collectively 



A. Different kinds of pollen grains, highly magnified, two 

 of them forming tubes. (After Duggar.) 



B, C. Parts of a stamen. 



A, front; B, back; a, anther; c, connective; /, filament. 

 (After Strasburger.) 



D, E, F, Modes of discharging pollen. 



A, by longitudinal slits in the anther cells (amaryllis) ; B, 

 by uplifting valves (barberry) ; C, by a pore at the top of each 

 anther lobe (nightshade). (After Baillon.) 



as the anther. When mature, the sporangia split longitudinally and 

 permit the escape of the pollen. 



There are two series of leaf-like structures below the structures we 

 have just been discussing. These two series together form the perianth. 



