ONION SMUT FUNGUS. 



119 



A. Section through a resting 



seed. 



B. Longisection of a seedling 



four days after planting. 



C. Successive stages in the de- 



velopment from the third 

 day to the twenty-fifth 

 day. 



D. Diagrammatic longisection 



through the growing zone 



at the end of two weeks. 



Symbols for parts are the 



same in all: 

 sc, seed coat. 

 en, endosperm. 

 em, embryo. 

 lb, leaf bud or primordium of 



first leaf. 

 re, root cap. 

 r, radicle or first root. 

 en, cotyledon. 

 rj, root joint. 

 kn, knee. 

 al, ascending leg. 

 dl, descending leg. 

 CO, exterior opening of coty- 



ledonary cavity. 

 rS and r3, first and second 



secondary roots. 

 cc, cotyledonary cavity. 

 gp, growing zone, region of 



origin of all leaves and 



roots. 

 Ib2, primordium of second 



leaf. 



Fig. 3. — Development of an onion seedling. 



