Seeds And seedlings 



75 



at first they seemed to serve as leaves, later becoming absorbed 

 as food by the growing seed. In the pea the cotyledons serve as 

 food, but remain under ground. In the corn the single cotyledon 

 serves as an organ for digesting and absorbing food from the 

 storehouse of food known as the endosperm. 



Monocotyledons and Dicotyledons. — Plants that bear seeds 

 having but a single cotyledon are called monocotyledons. The corn 

 is an example of such a plant. Although we find a good many 

 monocotyledonous plants in this part of the world, this group is 

 characteristic of the tropics, just as the dicotyledons are the type 

 for the temperate climate. Sugar cane and many of the large 

 trees, such as the date palm, palmetto, and banana, are examples. 

 Among the common monocotyledons of the north temperate zone 

 are corn, lily, hothouse smilax, and asparagus. 



Polycotyledons. — A third type of plant, grouped according to 

 the number of cotyledons, is the group represented by the pines 

 and their kin. 



Pine seedlings may be grown in damp moss or sawdust. They must be 

 started at least three weeks before they are needed for use in the laboratory.^ 



The Pine Cone and its Seeds. — Ma- 

 terial should be gathered in the fall 

 and early summer. Get some very 

 young cones and some of older 

 growth that contain seeds. The 

 pine tree bears inconspicuous flowers 

 of two kinds, pollen-bearing and 

 seed-forming. Pollination is accom- 

 plished by the wind, the cones grow- 

 ing as the result of fertilization. 

 Notice the position of the cone on 

 the branch. Compare a young cone 

 with an old one. You will find in 

 the young cones that the scales are 

 green in color and are cemented to- 

 gether by the sticky resin or pitch. 

 In the older cones the seeds are 

 ready for dispersal. They usually 

 take two summers to grow to ma- 

 turity. Pull back one of the scales 

 making up the cone and see what 

 happens. How is the seed adapted to 

 be scattered? Draw one of the scales ^ , , • i 



of the cone and a winged seed to show the position of the seed when in place. 



If you cut open a seed lengthwise, after having split the hard outer coat, 

 you wiU find the tiny embryo in the center of the seed, surrounded by its 



1 See Hunter and Valentine, Manual, page 75. 



Spruce cone and scale containing winged 

 seed. Photographed by Overton. 



