STUDIES OF SEED-PLANTS 151 



In order to identify the parts of the embryo, it is best co examine 

 first some stages in germination. 



Examine a corn seedling just coming out of the soil. Only the 

 epicotyl appears as a coil of leaves rolled up with the younger leaves 

 within. Dig up such a seedling, or study a similar one grown 

 on moist paper, and notice that the root or roots and the epicotyl 

 grow from the embryo part of the grain. Make a drawing of such 

 a stage. The part of the embryo which still remains embedded in 

 the endosperm is thought to be the single cotyledon, which remains 

 within the seed-coat as an organ to digest the endosperm and then 

 to absorb the digested substances and transfer them by osmosis to 

 the growing parts of the seedling. 



The first root appears at the end of the grain which was attached 

 to the cob. Look for it in grains before germination begins and 

 label it hypocotyl in drawings. Recall that the hypocotyl in bean 

 and squash seeds consisted of two parts or regions, stem and root 

 (consult your drawings). Could the corn grain remain in the ground 

 if part of the hypocotyl grew into an elongated stem (that is, a stem 

 between root and cotyledons) as it does in bean and squash ? Write 

 a brief paragraph comparing the corn grain and pea seed with 

 regard to behavior of epicotyl, cotyledons, and hypocotyl. 



Make transverse and longitudinal cuts through water-soaked 

 (or preserved "green") grains of corn. Identify endosperm, 

 hypocotyl, epicotyl, and cotyledon by comparing with germination 

 stages studied as above. Make sketches. 



140. Other Seeds. The following are suggested for study by 

 pupils who satisfactorily complete the preceding lessons in advance 

 of the class. Use dry and water-soaked seeds and seedlings in 

 various stages of germination as in preceding lessons. Grow some 

 in flower-pots. Look for the same parts of embryos and compare 

 their development as the seeds germinate. Make drawings and 

 compare similar seeds. 



Sunflower Seed. The so-called "flower" of the sunflower plant 

 is really a group or head of small flowers, and each flower forms one 

 "seed." The hard seed-case is wall of ovary, corresponding to pod 

 of bean. The inside delicate coat is the real seed-coat correspond- 

 ing to that of a bean. Find two cotyledons, hypocotyl, and epi- 

 cotyl. Compare germination with that of squash seed. 



Four-o'clock Seed. One flower produces one seed and the outer 

 coat is wall of ovary. The two large cotyledons are folded around 

 a central mass of white endosperm. Compare with position of 

 endosperm in castor-oil seed. 



