PRACTICAL WORK 387 



ing and increasing the aerial shoot from year to year, 

 thus permitting of that great increase in the bulk of 

 the body which has given us the trees, the dominant 

 plants over a large part of the earth's surface, the 

 production of ovules and seeds has enabled the higher 

 plants almost to cover the face of the globe. 



PRACTICAL WORK. 



Seeds and Seedlings. 



A. THE BROAD BEAN ( Vicia Faba) : a seed without endosperm 



and with hypogeal cotyledons. 



(1) Make drawings of the side and front views of the seed 

 showing the long scar of attachment to the pod and the position 

 of the micropyle at one end of the scar. [By squeezing a bean 

 which has been thoroughly soaked a drop of water can be forced 

 out through the micropyle.] Pull the testa from a soaked bean 

 to show the embryo, which completely fills the seed. Detach 

 carefully one of the massive cotyledons, and draw the internal 

 surface of the other with the curved epicotyl and the straight 

 radicle at one side. 



(2) Sketch a series of germinating seeds and seedling in different 

 stages, marking cotyledons, epicotyl, foliage leaves (the lowest 

 are rudimentary), axillary buds, terminal bud, primary root, 

 lateral roots. The hypocotyl remains short. 



B. THE VEGETABLE MARROW (Cucurbita) : a seed with perisperm 



and thick epigeal cotyledons. 



(3) Note the flatness of the seed, the scar of attachment (pit- 

 like) and the adjacent micropyle. Split the seed lengthwise 

 and observe the greenish layer of perisperm (nucellus), two rather 

 thick cotyledons (though much thinner than in the bean), with 

 very minute epicotyledonary bud between, and radicle. 



(4) Make a series of sketches from stages illustrating the 

 elongation of the hypocotyl, the pulling of the cotyledons from 

 the testa, the straightening of the hypocotyl and the expansion 

 and greening of the cotyledons. Mark the various organs of 

 the seedling, the epicotyledonary leaves differing in shape from 

 the cotyledons and the " peg " or " heel " at the base of the 

 hypocotyl, which holds down one valve of the testa while the 

 cotyledons are extracted. 



