62 



BOTANY. 



their real nature can be made out. In their simplest form 

 they are the small irregular spaces which appear during the 

 rapid growth of parenchyma-cells (Fig. 40) ; from these to 

 the large regular canals which are common in many water- 

 plants there are all intermediate gradations. 



Fio. 40.— A bit of the soft tissue of thepith of the stem of Indian corn ; 

 transverse section, giu, simple plate of cellulose, forming the partition-wall 

 between two cells ; 2, z, intercellular spaces caused by splitting of the 

 walls during rapid growth. Magnified 550 times. 



109. In leaves, especially in the soft tissue of the under 

 portion, there are usually many large irregular spaces be- 

 tween the cells ; they are in communication with the exter- 

 nal air through the breathing-pores, and contain only air 

 and watery vapor. The leaf-stalks and stems of many 

 aquatic plants contain exceedingly large air-conducting in- 

 tercellular canals, which occupy even more space than the 

 surrounding tissues (Fig. 41). In the rushes, water-lilies, 

 and water-plantains they are so large as to be readily seen 

 by the naked eye. These all are in communication with 

 the external air through the breathing-pores and the inter- 

 cellular spaces of the leaves. 



110. Some intercellular spaces serve as reservoirs of gum- 

 my or resinous secretions. Such ones are surrounded by 



