366 THE STRUCTURE OF ECONOMIC PLANTS 



Embryogeny. — Studies of embryogeny in the Leguminosae 

 indicate that there are many variations in the details of embryo 

 development. Guignard (14) has pointed out that these are due in 

 part to significant differences in the character of the suspensor 

 and the shape of the proembryo in the early stages of embryogeny. 

 However, Martin (18), working with Trifolium (three species), 

 Medicago, and Vicia, found that all five were alike in the develop- 

 ment of the integument of the ovule, in the production of four 

 megaspores, and in the rapid destruction of the nucellar tissue in 



/— a6 V 



— -0 w 



^--ad V 



Fig. 185. Longisection of portion of carpel showing orientation of developing ovules: 

 ab V, abaxial vein ; ad v, adaxial vein ; emb sac, embryo sac ; / int, inner integument ; mk, 

 micropyle; o int, outer integument; o w, ovary wall. 



embryogeny, indicating that certain groups of legumes may be 

 very similar in their developmental behavior. 



According to Cooper (6), fertilization occurs in the late bud 

 stage about ix to i4 hours before the open flower stage. Following 

 fertilization, the first division of the zygote is transverse, and at 

 this two-celled stage the endosperm may be two or four nucleate. 

 This occurs in the open flower stage and by the time the flower has 

 withered, the proembryo is four-celled, the division of the basal cell 

 being longitudinal. The true embryo develops from the apical 

 cell of the four-celled proembryo while the two basal cells form 

 much elongated, multinucleate structures which, with the deriva- 

 tives of the middle cell, constitute the suspensor. The middle cell 

 also divides longitudinally, and the daughter cells likewise become 

 multinucleate, much enlarged and globular. These four multi- 

 nucleate cells disintegrate as the cotyledons develop. 



