456 THE STRUCTURE OF ECONOMIC PLANTS 



lae that are more or less evident in the form of warty protuberances. 

 The cells of the epicarp or outer epidermis are small and isodia- 

 metric, and in surface view, are sinuous in outline. The oil ducts 

 in the mesocarp are surrounded by a layer of polygonal cells which 

 become brownish at maturity, and the bundles located in the ribs 

 are accompanied by groups of sclerenchymatous cells. The some- 

 what elongated cells of the inner layer of the mesocarp are broader 

 than those of the endocarp. Winton states that they are usually 

 transversely oriented, but that it is not uncommon for them to be 

 arranged with their long axes in other directions. The endocarp 

 or inner epidermis is composed of narrower cross cells, which are 

 transversely elongated or occasionally develop in a parqueted or 

 mosaic arrangement. 



The mature mericarps, each the product of the development of 

 one of the carpels, separate along the commissural line and are 

 suspended from a branched carpophore. This is a unique structure 

 peculiar to the fruit of the UmbelLferae and has been interpreted 

 by some investigators as being axial — that is, as a prolongation 

 of the receptacle between the carpels. Others regard it as being 

 appendicular and derived from portions of the two carpels. Jack- 

 son (9) has studied the structure on the basis of its development in 

 the flower and fruit and has concluded that 



"a small basal portion is usually receptacular or axial; by far the 

 greater part is appendicular. ... It represents an innermost, ventral 

 portion of the two carpels and consists chiefly of the ventral traces 

 of these carpels. Associated with the traces in the formation of this 

 structure is a greater or lesser amount of adjacent non-vascular tissue." 



In the mature fruit, the point of separation of the mericarps from 

 the carpophore begins at the level at: which the stele of the recep- 

 tacle branches to form the peripheral and central bundles. The 

 peripheral bundles constitute the vascular supply for the two 

 mericarps, while the two central bundles form the carpophore. 

 This consists of the two bundles, the large lignified parenchymatous 

 cells which lie between them, and some non-lignified parenchyma 

 which dies as the carpophore and fruit mature. The break which 

 separates the carpophore into two branches occurs in the lignified 

 parenchyma between the central bundles so that each carpophore- 

 half consists of one central bundle. 



The seed has a thin coat consisting of an outer layer of large 

 cells and an inner zone of several rows of crushed cells. The cells 



