SEEDS AND SEEDLINGS. 



45 



and plumule. You will find that most seedlings show this 

 epigeal type of growth epigeal meaning that the coty- 

 ledons come above the soil, while only a few besides 

 Broad Bean and Scarlet Runner have hypogeal (below 

 ground) cotyledons. It is simply a question of whether or 

 not the hypocotyl grows in length. You will also notice 

 that epigeal cotyledons sooner or later turn green, grow 

 larger and thinner, and are more like foliage-leaves than in 



A B C D c 



Fig. 22. French Bean. A and B are views of the entire seed ; to F are views of the 

 embryo (seed-coat removed) ; G to L are stages in germination. 



the case of hypogeal cotyledons, which do not turn green 

 (unless they happen to be exposed to the light) and which 

 soon shrivel up. 



Notice that in the different species of Phaseolus (Dwarf 

 and Climbing French Beans, Scarlet Runners) we get a 

 transition from the hypogeal to the epigeal type. Note 

 that in these plants the first two foliage-leaves are simple 

 and heart-shaped and stand opposite each other, while the 

 later leaves are compound, having three leaflets, and arise 

 singly from the stem; what other differences do you notice 

 between the first and the later leaves, and between the hypo- 

 cotyl and the axis of the plumule ? 



