PROBLEM 3 . How Complex Plants 



scatterinor the seeds over a wide area. 

 The outside agents that help in this seed 

 dispersal are wind, water, birds, and 

 other animals, including man. You prob- 

 ably can give numerous examples of seed 

 dispersal. Do Exercise io. 



The life cycle of the flowering plant. 

 At certain times the flowering plant pro- 

 duces flowers containing stamens and 

 pistils. The stamens produce pollen 

 grains which later produce sperms in 

 the pollen tube. The ovary contains 

 ovules each of which forms an egg in the 

 embryo sac. Fertilization occurs within 

 the embryo sac after pollination and the 

 growth of the pollen tube. The fertilized 

 egg cell then develops into the embryo. 

 The ovule which contains the fertilized 

 egg grows into the seed. The ovary 

 grows into the fruit. During the growth 

 of the ovary into a fruit the petals wither 

 and usually fall off. Gradually the fruit 

 and the seeds within it ripen on the plant. 

 The ripe seeds later drop to the ground, 

 sometimes while still in the fruit. There 

 they may rest over the winter. When 

 conditions are favorable, the embryo 

 within the seed bursts through the seed 

 coats and grows into the seedling and 

 gradually comes to look like the parent 

 plant. In time this plant again bears 

 flowers and the cycle is repeated. The 

 organs which have been concerned in 

 one way or another with reproduction 

 are the flower, fruit, and seed. 



(Optional) Reproduction in ferns. 

 Ferns never bear blossoms. They pro- 

 duce spores by asexual reproduction. At 

 certain seasons the spore cases show 

 clearly on the lower surface of the frond 

 (leaf). See Figure 364. When the spores 

 ripen, they fall out of the cases and are 



Reproduce 



Fu;. 395 Fruits 

 and seeds. How 

 may each kind be 

 dispersed? 



MILKWEED 



BURDOCK 



DANDELION 



MAPLE 



(AMERICAN MU- 

 SEUM OF NATURAL 

 HISTORY; SCHNEI- 

 DER & SCHWARTZ; 

 BROOKLYN BOTANIC 



garden) 



scattered on the ground. Because of their 

 thick walls, they do not die if the 

 weather is dry. When conditions are 

 favorable, that is, when it is moist and 

 warm, they germinate. 



But a spore does not grow into a new 

 fern plant. Instead, there is produced a 

 small, heart-shaped, green body (called 



