MEDICAGO SATIVA 



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of a linear row of six cells. (Fig. 159, A, B.) The embryo is 

 developed from the apical cell of the six-celled proembryo, while 

 the remaining cells produce the suspensor. 



The first division of the apical cell to form the embryo is, in most 

 instances, parallel to the long axis of the proembryo; and two 

 additional divisions, one vertical and the other transverse, result 

 in the formation of an eight-celled embryo. (Fig. 159, C, D.) 



Fig. 159. Stages in embryogeny : A, formation of four-celled proembryo; B, six -celled 

 proembryo ; C, two-celled embryo with five-celled suspensor ; D, eight-celled embryo with 

 eight-celled suspiensor; E, initial differentiation of cotyledons, epicotyl, and hypocotyl 

 with suspensor at stage of greatest development ; F, initiation of curvature of embryo in 

 region of epicotyl, the suspensor is disintegrating; G, mature embryo with portion of upper 

 cotyledon removed to show stem tip and leaf primordia : cof, cotyledon ; eel, epicotyl ; hyp, 

 hypocotyl; /.leaf; st, stem tip, j-«j, suspensor. (Redrawn and adapted from Cooper, /w/r. 

 Agr. Res.^ 



Subsequent periclinal divisions cut off the dermatogen layer, and 

 continued growth results in the formation of an embryo which is 

 at first spherical and later elongates and broadens at its apex. 

 In the development of the hypocotyl and cotyledons, the former 

 elongates, and this is followed by a curvature of the embryo so 

 that the hypocotyl and cotyledons lie approximately parallel at 

 maturity. (Fig. 159, E, F, G.) There is an early differentiation 

 of the provascular strands, and the advanced condition of the mature 

 embryo is evidenced by the presence of the foliage leaves. 



