174 MORPHOLOGY AND LIFE HISTORY 



K. The Seed: 



1. The seed matures about July i. Study the struc- 

 ture of a ripe seed, comparing it in every point with 

 the structure of the unripe ovule, as directed above 

 (J, i-io). 



2. Note the soft, outer layer of the integument. 

 Describe it. 



3. In cutting away the hard, shell-like inner layer 

 (endopleura) be careful not to disturb the portion 

 of the nucellus that fits like a cap over the mycro- 

 pylar end of the endosperm. Now carefully lift 

 this portion of the nucellus and observe the long, 

 coiled suspensor attached to it, and (at its other 

 end) to the projecting thick, round peg (hypocotyl) 

 of the embryo. 



4. With the scalpel gradually remove one-half of the 

 endosperm, until you expose the embryo (young 

 sporophyte) imbedded in it. Is the embryo curved 

 or straight? Is it now confined to the venter of 

 the archegonium? 



5. Observe that the hypocotyl bears fleshy seed-leaves 

 (cotyledons). How many are there? Compare 

 their lengths. 



6. Does more than one embryo come to maturity in 

 any one seed? 



7. When the sporophyte of Zamia begins to develop, 

 is its growth continuous to maturity, or does a 

 period of rest intervene between two stages of 

 growth? Compare Zamia with the fern, moss, and 

 Selaginella in this respect. 



8. Define a seed, and state how it differs from an 

 unripe ovule, and from a spore. 



9. Suggest any advantage to the plant of the seed- 

 habit. 



