THE FLOWER AND FRUIT 107 



leaves. The fruit involves the entire inflorescence, and individual 

 fruits, which are pomaceous and fleshy throughout, are surrounded 

 by a fleshy mass developed from the bracts, sepals, petals, and 

 axis of the inflorescence. A somewhat different multiple type oc- 

 curs in the globe artichoke, Cynara, in which the axis terminates 

 in a globular head that is surrounded by numerous involucral 

 bracts. The heads, together with the bracts, are harvested when 

 immature; and the bases of the involucral leaves and the apex of 

 the inflorescence constitute the edible portion. 



The Seed. — In angiosperms, the seed consists of an embryo or 

 embryos surrounded by a covering which is generally integumentary. 

 Endosperm and nucellar tissue containing reserve foods may be 

 present; but, frequently, one or both of these tissues are lacking, 

 in which case the food reserves are stored in the cotyledons. 



Following pollination, fertilization is effected by the union of 

 one of the two microgametes and the megagamete. The resultant 

 zygote undergoes divisions which initiate the embryo sporophyte. 

 The development of the endosperm precedes or parallels embry- 

 ogeny and begins following the union of the second microgamete 

 with the polar nuclei to form the endosperm nucleus. The forma- 

 tion of endosperm tissue may proceed more rapidly than the devel- 

 opment of the embryo, and food reserves are accumulated in the 

 endosperm cells. The event of double fertilization probably 

 represents the point at which the seed may be differentiated from 

 the ovule; since, from that time, subsequent developments are 

 concerned directly with the embryogeny of the new sporophyte 

 generation and its related nutritive tissues. 



The Embryo. — The embryo in angiosperms consists of a hypo- 

 cotyledonary axis, one or two cotyledons (infrequently three or more 

 occur), and an epicotyl. The degree of epicotyledonary develop- 

 ment prior to the germination of the seed is variable. In some 

 cases (Pisum, Zea), the growing point of the epicotyl may differ- 

 entiate one or more leaf primordia above the cotyledonary node; 

 while, in others, it may consist of nothing more than a small mass 

 of meristematic cells. The growing point of the hypocotyl may 

 be organized as a well-defined primary root in which the histogens 

 and root cap are definitely determined; or it, too, may consist of 

 nothing more than a rudimentary terminal meristem. 



Embryogeny is extremely varied with respect to the details of 

 ontogeny. The descriptions given by Hanstein (8) for Capsella; 



