GROUPS OF TISSUES, OB TISSUE-SYSTEMS. 57 



with the external air through the breathing-pores and the 

 intercellular spaces of the leaves. 



Fio. 36.— Intercellular spaces. A, in leaf -stalk of a Water-lily; s, star-shaped 

 cells. B, in stem of a Rush: the cells here all star-shaped. Both cross-sections. 



Fio. 37.— Transverse sections of young stem of Ivy (Hedera helix). A, young 

 intercellular gum-canal, surrounrfed by four cells; c, cambium; B, fully devel- 

 oped canal, g\ &, bast. Magnified 800 times. 



108. Some intercellular spaces serve as reservoirs of gum- 



