56 



BOTANY. 



are intercellular and which at no time -were composed of 

 cells. In some cases they so closely resemble the cavities 

 derived from cells that it is with the greatest difficulty 

 that 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. 35); 

 from these to the large regular canals which are common 

 in many water-plants there are all intermediate gradations. 



Via. 35.— A bit o£ the soft tissue of the pith of the stem of Indian com ; trans- 

 verse section, gw, simple plate of cellulose, forming the partition-wall between 

 two cells; z, z, intercellular spaces caused by splitting of the walls during rapid 

 growth. Magnified' 550 times. 



101. 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 

 intercellular canals, which occupy even more space than 

 the surrounding tissues (Fig. 36). 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 



