114 THE STRUCTURE OF ECONOMIC PLANTS 



as lateral lobes on either side of the growing point of the epicotyl. 



(Fig. io6, P.) 



Concurrent with the development of the embryo, an abundant 

 endosperm is formed which fills the embryo sac. This is gradually 

 utilized by the embryo, which develops a curvature corresponding 

 to the contour of the embryo sac. Some of the endosperm still 

 remains in the seed at maturity, surrounding the embryo and 

 occupying the region between the primary root and the cotyledons. 

 (Fig. io8, /4.) Twin embryos have been reported by Savelli (14). 



Histology of the Fruit and Seed. — The fruit is an akene 

 which is light brown to dark gray, or in some cases mottled. It 

 is smooth, somewhat compressed, and orbicular or oval in form; 

 but varies in this respect and in size, as does the enclosed seed. 

 Heuser (15) reports the average length of the pointed types as 

 4.3 mm., with diameters ranging from 1.75 to 3.3 mm.; and Dewey 

 (ii) records the length of the fruit as from 3 to 6 mm. with diame- 

 ters of from 1.5 to 4 mm. 



The "seed" of commerce is actually the fruit which in some cases 

 comes into the market enclosed within its hooded floral bract. 

 (Fig. 107, A.') The outer epidermis of the floral bract is charac- 

 terized by its hairs and glands. The hairs attain a length of 0.5 to 

 i.o mm. and taper abruptly or gradually to a pointed apex from 

 spherical bases which contain cystoliths of calcium oxalate. The 

 globular gland consists of eight or more cells radiating from two 

 central ones which may be sessile; but, in most cases, they are 

 borne on many-celled stalks. (Fig. 107, D.) The secretory cavity 

 is formed by the separation of the outer cuticle from the terminal 

 cells. 



The pericarp of the fruit, which is comprised of five distinct 

 regions, has been described by Winton (19). The outermost 

 zone, or epicarp, is a layer of sclerenchymatous cells which are 

 sinuous in outline as seen in surface view. Their radial walls are 

 only slightly thickened in some regions; while, in others, they 

 are so thick that the lumen of the cell is much reduced. All the 

 walls of this layer are porous. The second region of spongy paren- 

 chyma consists of one or more layers of colorless cells between 

 which there are many intercellular spaces. Numerous anastomos- 

 ing bundles, that can be seen through the epicarp, extend through- 

 out this layer, which is thicker along the two keels of the fruit. 

 (Fig. 107, B.) Underlying the hypodermal layers are the brown 



