THE SEED AND ITS GERMINATION 



= -cot 



seed ■where the latter was attached to its place of growth in the 

 squash. Label this hilum. Note the little hole in the hilum ; it is 

 the micropyle, seen most plainly in a soaked seed. (If there are two 

 depressions on the hilum, the deeper one is the micropyle.) 



Describe the color and texture of the outer coating of the seed. 

 With a scalpel or a very sharp knife cut across near the middle a 

 seed that has been soaked in water for twenty- 

 four hours. Squeeze one of the portions, held 

 edgewise between the thumb and finger, in 

 such a way as to separate slightly the halves 

 into which the contents of the seed is naturally 

 divided. Examine with the magnifying glass 

 the section thus treated, make a sketch of it, 

 and label the shell or covering of the seed and 

 the kernel within this. 



Taking another soaked seed, chip away the 

 white outer shell called the testa, and observe 

 the thin, greenish inner skin (Fig. 1, e), with 

 which the kernel of the seed is closely covered.^ 



Strip this off and sketch the uncovered ker- 

 nel or embryo. Note that at one end it tapers 

 to a point. This pointed portion, known as 

 the hypocotyl, will develop after the seed sprouts 

 into the stem of the plantlet, like that shown 

 at c in Fig. 9. 



Split the halves of the kernel entirely apart 

 from each other, noticing that they are only 

 attached for a very little way next to the hypo- 

 cotyl, and observe the thickness of the halves 

 and the slight unevenness of the inner surfaces. 

 These halves are called seed-leaves or cotyledons. 



Have ready some seeds which have been soaked for twenty-four 

 hours and then left in a loosely covered jar on damp blotting paper 

 at a temperature of 70° or over until they have begun to sprout. 



Split one of these seeds apart, separating the cotyledons, and 

 observe, at the junction of these, two very slender pointed objects, 

 the rudimentary leaves of the plumule or first bud. 

 1 See Sect. 15, page 13. 



Fig. 1. Lengthwise 

 Section of a Squash 

 Seed. (Magnified 

 about two and a 

 half times.) 



c, hypocotyl; cot, coty- 

 ledon; e, endosperm; 

 li, hilum ; p, phimule; 

 t, testa. 



