414 Mr. Bowman on the Parasitical Connection 



admirably adapted to their peculiar circumstances and situation. 

 Had the cuticle been furnished with air-valves, the soil would 

 have continually clogged and impeded their office ; they are 

 therefore removed by a contrivance, as beautiful as wise, and 

 placed within the convoluted chambers excavated for them in the 

 interior of the leaf, where they perform securely and unseen their 

 destined office. If it be doubted whether, from the unusual 

 form and prominence of these papillae, they are the real ab- 

 sorbents of the leaves, I would hint the probable advantage of 

 some such arrangement to enable them more effectually to act 

 upon the very small supply of air admitted into the cells, which 

 is, moreover, always in a stagnant state. It will not, I think, 

 be contended that they absorb moisture rather than air ; and as 

 this forms the grand distinction between roots and leaves, I trust 

 I have satisfactorily proved them to be the latter ; though, be- 

 cause their functions are performed in the dark, one material 

 effect of these organs is not produced. 



The succulent or solid portion of the leaves also deserves atten- 

 tion from its singularity of structure. It consists altogether of a 

 framework of cellular substance, chiefly in hexagonal compart- 

 ments, resembling a number of hollow dodecahedron crystals 

 closely fitted together (see the sections. Tab. XXIII. Fig. 10. & 

 11.). Each cavity, besides the watery juice which fills it, contains 

 several oval or pear-shaped and perfectly transparent bladders, 

 quite detached from each other and from the sides of the cells, and 

 lying over one another in an irregular manner (see Tab. XXIII. 

 Fig. 13.). They are from their minuteness invisible to the naked 

 eye, but exhibit a very curious appearance in a thin section of the 

 leaf under the compound microscope. In one of these sections, 

 placed between the talcs of an ivory slider in April 1828, they 

 still retain their original shape and size ; from which I at first 

 concluded they were distended with air. Subsequent experi- 

 ments 



