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 («) and 

 shallow receptacle formed by 

 the "nectary" (o). Note bundle 

 of conducting tissues (x), — ■ 

 After Bonnier. 



Fig. 634. — Flower of nastur- 

 tium (Tropaeolum ma jus) cut 

 through the middle to show the 

 spur {s) and the nectar (»). 



Fig. 635. — Nectar gland in the 

 ovary of day lily {Hemerocallis 

 flava). — After Schniewind-Thies . 



