SEEDS AND THE MORPHOLOGY OF SEEDLINGS. 



I. COMMON BEAN (Phaseolus vulgaris). 

 The Seed. 



The point of attachment to the pod is the hilum. 



A minute opening on one side of the hilum is the micropyle. 



A slight ridge running from the opposite side of the hilum to- 

 ward the end of the seed is the rhaphe. The ovule of the Com- 

 mon Bean is amphitropous. The seed is also amphitropous but 

 the parts are more or less obscured by growth. 



Where the rhaphe disappears near the end of the seed is the 

 chalaza. 



These parts, although evident in this seed, are usually more 

 prominent in the ovule than in the seed. 



Split the seed in two through the hilum and rhaphe. 



Kach half is one of the large cotyledons. 



A small white cylindrical body lies imbedded between the 

 cotyledons with its free end at the micropyle. This is the hypo- 

 cotyl. This organ is called by some the " radicle " ; by others the 

 "caulicle." 



The point where the cotyledons are attached to the hypo-cotyl 

 is the first node. 



Midway between the upper and lower sides of the cotyledon 

 and near one end is a body, fish-tail in shape. This is the rudi- 

 mentary first pair of leaves. 



Between the base of the first pair of leaves and the first node 

 is the first internode. 



The first internode and the first pair of leaves, together con- 

 stitute the plumule. The plumule is unusually developed in the 

 seed of the Bean. 



The cotyledons, hypocotyl, and plumule, together constitute 

 the embryo. 



This seed is ex-albuminous. 



The outer-seed-coat ox testa is brittle and highly polished. 



