24 



PRELIMINARY STUDIES. 



In a typical complete flower each of the parts is sepa- 

 rate, all being inserted on the torus. The greatest variety 

 of variations from this type occur. The pistils are fre- 

 quently united through the whole or a part of their 

 length; so also the stamens. If the petals are separate, 



the flower is polypetalous ; if 

 united, as in the Mayflower, 

 Blueberry, and Rhodora, the 

 flower is gamopetalous. If the 

 sepals are separate, the flower 

 is polysepalous ; if united, as in 

 Ground Ivy, Locust, Carnation, 

 Bouncing Bet, Toad Flax, the 

 flower is gamosepalous. Some 

 flowers are both gamopetalous 

 and gamosepalous, as the Bluet, 

 Partridge Vine, Harebell, Twin 

 Flower, and Fringed Gentian. 



23. The .fertilization of the 

 flower. Before the flower can 

 perform the function for which 

 it was designed, namely, pro- 

 duce seed, it must be fertilized. 

 Pollen grains from the same or 

 different flowers are brought in 

 contact with the stigma. Here 

 they begin to grow and send 

 down long tubes through the 

 style to the ovaries. The con- 

 tents of the pollen grains pass 

 down through these tubes and enter certain cells in the 

 ovaries. These cells, the ovules, then develop into seeds. 

 The micropyle, already observed on the Bean and Pea, 

 marks the place where the pollen tube entered the ovule. 

 Even when flowers have both stamens and pistils, self 



FIG. 3. Diagram of a longitu- 

 dinal section of an ovary 

 having only one ovule with 

 basal placentation, designed 

 to exhibit the course of the 

 pollen tube from the stigma 

 to the summit of the embry- 

 onal sac above the ob'sphere. 

 The ovule is anatropous, and 

 is inserted, as is usually the 

 case in Composite. (Luers- 

 sen.) 



