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 papille, 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, þe- 
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, Tas. 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 ofthe cells, and | 
lying over one another in an irregular manner (see Tas. XXIII. 
Fig.13.). They are from their minuteness invisible to the naked 
eye, but exhibita 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 
Ad. RS Sao iiis cu ey ği 
ER ue nte 
