THE DIFFERENTIATION OF FLOWER-BUDS 37 



toward the outer edge and a short way down the sides of the 

 cone or cyhnder-Uke growth. The tissue beneath these 

 embryonic regions is differentiated into pith cells and vas- 

 cular bundles, and inclosing all is the epidermis. 



37. Sepals. — A rapid multiplication of the cells at the 

 outer edge of the near upper surface of the bud results in the 

 formation of a slightly elevated ridge, the torus or receptacle. 

 (See Fig. 16.) Growth takes place more rapidly at five points 



ca\yx priTTiordia 

 eoLge of 



Fig. 16. — Diagramma- 



FiG. 15. — Diagram tic representation of 



indicating positions origin of calyx pri- 



of four flower pri- mordia on edge of 



mordia. torus. 



about equally spaced on this ridge, and thus the primordia 

 of the sepals are begun. 



Because of the increase in number and size of the cells 

 below and between the calyx primordia, the torus or recep- 

 tacle of the flower continues development, particularly 

 toward the outer edge, with the result that this outer portion 

 is arched up and the calyx-lobes are elevated along on top of 

 it. The petals, stamens, and carpels arise from the concave 

 side of the toi-us, and the meristematic tissue out of which the 

 primordia of these organs are finally differentiated exists as a 

 sort of lining beneath the epidermis of the cup-like torus. 

 As development continues, the sepals enlarge and become 

 inclined toward one another at the apex, until they interlap 

 and form a tent-like structure over the depression below 

 them. When the period of winter rest arrives, these parts 



