588 CONSERVATIVE ORGANS. [LECT. X. 



This difference, as shall afterwards be explained, is 

 probably necessary for the distinct functions of 

 these two surfaces ; and thence, in every attempt 

 to theorize on the structure of parts, the pro- 

 priety of keeping in view the fact, that plants as 

 well as animals are living beings, and consequently 

 not regulated by those laws which control the 

 configuration of inanimate matter. No plant is 

 better adapted than the Christmas Rose, Helle- 

 borus niger, to demonstrate this diversity of cel- 

 lular structure in the same leaf. If we examine 

 a thin transverse slice of a leaf of this species 

 of Hellebore, with a good magnifying glass, we 

 perceive that, immediately under the cells of the 

 cutis (31. a.), which are large and oval, there is a 

 range of tubular cells (b.) terminating in the true 

 pulp or parenchyma of the leaf (c.) ; which con- 

 sists of irregular hexagonal cells, and occupies the 

 whole of the space between the tubular cells and 

 the cuticle (d.) of the under disk of the leaf. Under 

 the highest power of the microscope, we find that 

 these tubular cells (32. b.) have apparently a di- 

 rect communication with the cells (a.) of the 

 cutis ; and also with the range of cells (c.) im- 

 mediately beneath them: but in neither are 

 the mouths open, for, a membrane bounds the 

 oblong cell in every direction. In the trans- 

 verse section of some leaves, as for instance those 

 of Calla j&thiopica (33.), which is an aquatic 



