LKCT. X.] ANATOMY OF LEAVES. 589 



plant, we find several ranges of tubular cells 

 (b.) commencing under the cutis (a.) of the su- 



perior disk. Some of these terminate in the hex- 

 agonal cells (d.), and others in empty cavities 

 (f*f.) y such as are present in the leaves and the 

 petioles of all aquatic plants, and which, being filled 

 with air, seem intended for enabling them to rise 

 above or to float on the surface of the water. 

 Under the microscope these tubular cells (34. b.) 

 in the leaves of Calla, resemble a chain of short 

 vessels, with valvular partitions; and were, in- 

 deed, erroneously regarded as such by Malpighi 

 and Leuwenhoek, who observed them in the 

 stem. But these cells are not furnished with open 

 mouths, nor with valves, neither where they 

 originate in the cuticular cells (34. a.), nor at their 

 union with each other, nor where they termi- 

 nate (d.) in the common pulp of the leaf; and 

 this is the case, also, in all leaves furnished with 

 tubular cells. When the tubular cells are cut 

 transversely, they appear to be of an hexagonal 



