28 THE VEGETATIVE ORGANS 



the stalk below the cotyledon (hypocotyl, Fig. u, hy) 

 grows in such a way as to bend in the form of a crook and, 

 continuing to elongate, carries the cotyledons and the split 

 fruit-coat above ground. The cotyledons now separate, 

 throw off the fruit- and seed-coats, and turn green. 



Seeds of the Vegetable Marrow should be sown with 

 their flat faces horizontal ; in a few cases cut away a third 

 of one side of the seed-coat at the micropylar end and sow 

 these with the cut surface downwards, and determine the 

 mode of emergence of the plumule in each case, and note 

 how it separates from the seed-coat. As the radicle 

 emerges and turns downwards from the uninjured seeds, 

 a peg is formed on the under side, at the base of the hypo- 

 cotyl, which fixes the lower edge of the split seed-coat and 

 holds it down. The hypocotyl above elongates, the upper 

 half of the seed-coat splits off, and the cotyledons are with- 

 drawn and carried above ground, where they expand as 

 two flat, oval, green leaves. In those cases where part of 

 the seed-coat has been removed, the peg is unable to act 

 as holder, and the cotyledons, unable to extricate them- 

 selves, carry the seed-coat upwards, and it is only thrown 

 off when the cotyledons expand. The use of the peg, 

 therefore, is to enable the cotyledons and plumule to free 

 themselves more readily from the seed-coat. The position 

 of the peg is always on the under side, and, like the down- 

 growth of the radicle, is determined by gravity. 



Two modes of germination are seen in these types. In 

 the Bean, Edible Pea, and Sweet-Pea, the seed remains 

 below ground and only the plumule grows into the air ; this 

 mode of germination is known as hypogeal (Gr. hypo 

 = beneath, ge = earth). In the Kidney-Bean, Mustard, Cress, 

 Sunflower, Vegetable Marrow, Common Ash, and Syca- 

 more, the part of the stalk below the cotyledon (the hypo- 

 cotyl) grows and carries the cotyledons and plumule 

 together into the air. In these cases the cotyledons turn 



