Respiration, Aeration, and Fermentation 293 



of gases; sometimes indefinite air chambers form in a 

 variety of ways. The intercellular spaces are produced 

 by the splitting 

 apart of the walls 

 separating mer- 

 istematic cells, 

 generally at the 

 angles. In this 

 way, small 

 spaces are pro- 

 duced into which 

 air diffuses, and 

 when such spaces 

 are numerous, 

 they form practi- 

 cally continuous 

 air chambers. 

 In some cases 

 these spaces oc- 

 cupy far more 

 volume than the 

 cells themselves. 

 This is particu- 

 larly true in the 

 case of the mes- 

 ophyll tissue of leaves. 



Very large air spaces are a characteristic feature of many 

 water plants, and they are often accompanied by a pecul- 

 iar distribution of the cells, or of irregular or stellate 

 out-growths from these into the cavities at a later period. 

 Again, during the process of growth, cavities may arise 



FIG. 74. Experiment suggesting the efficient 

 aeration of the leaf. [After Detmer.] 



