THE MATERIAL OUTGO OF PLANTS 



339 



cane sugar, are known to be re- 

 tained ordinarily by the cyto- 

 plasm ; yet nectar glands secrete 

 sugar one or more times. Others, 

 for example 'enzymes, have a com- 

 position which, though imper- 

 fectly known, is such as to suggest 

 that the cytoplasm would usually 

 be impermeable to them; yet di- 

 gestion occurs in such places as to 

 make it certain that enzymes are 

 able to pass out of the cells in 

 which they arise. 



FIG. 633. Section through a 

 petal of buttercup (Ranunculus), 

 showing nectar gland (n) and 

 shallow receptacle formed by 

 the " nectary " (a). Note bundle 

 of conducting tissues (#). 

 After BONNIER. 



FIG. 634. Flower of nastur- 

 tium (Tropaeolum ma jus) cut 

 through the middle to show the 

 spur (5) and the nectar (n). 



FIG. 635. Nectar gland in the 

 ovary of day lily (H emerocallis 

 flava) . After SCHNIEWIND-THIES. 



