WffAT IS A SEED? 



333 



Pig. 352. 

 Parts of common bean. 



409. We are now curious to know if there is 

 anything in the structure of the embryos to 

 suggest the different behaviors of 

 the two beans in Figs. 348 and 

 349. Fig. 352 shows the coty- 

 ledons of a common bean laid 

 open; and Fig. 353 is a simi- 

 lar picture of the Scarlet Run- 

 ner bean. The node, or place 

 of attachment of the cotyledons, 

 is at C (one cotyledon, of course, 

 having been broken away). The 

 caulicles are the parts pointing 

 downwards, and the two leaves of the plumule 'lie 

 at the left. The observer will see that the space 

 between C and the plumule 

 is very different in the two 

 beans. These different 

 lengths are suggestive of 

 what takes place in germi- 

 nation, — the greatest elon- 

 gation of the stem in the 

 common bean takes place 

 beneath the cotyledons, 

 whereas the greatest elon- 

 gation in the Scarlet Run- 

 ner takes place above the cotyledons: in one case 

 the caulicle elongates, in the other it does not. 



Flu. 353. 

 Parts of Scarlet Runner bean. 



