ANATOMY AND PHYSIOLOGY Of PLANTS. 219 



5. It is a soft and juicy substance, constituting the 

 principal mass of succulent plants, and a great pro- 

 portion of many parts even of woody plants. It is also 

 very conspicuous in the leaf and flower, with their foot- 

 stalks, when stripped of the epidermis. 



When viewed without the microscope, its appearance is tUat of 

 an assemblage of small and minute granules imbedded in a soft and 

 glutinous substance, as in the greater part of leaves and succulent 

 fruits, in which last, the fracture often presents an appearance re- 

 sembling that of a piece of lump-sugar, as in the case of the apple 

 and pear. But when inspected minutely with a good glass, its 

 structure is found to be very different. 



6. Many excellent experiments have been made to 

 ascertain the real structure of this tissue, but the descrip- 

 tion which is said to be most correct, and the most ap 

 plicable, is that of M. Mirbel. 



Malpighi and Grew were the first vegetable anatomists who in- 

 vestigated the structure of the pulp ; and their experiments were 

 followed by those of Du Hamel, Saussure, Comparetti, and others, 

 but none have given so clear and plausible a result as M. Mirbel'a. 



7. Mirbel describes the cellular integument as com- 

 posed of cells similar to the geometrical cells of a 

 honey comb, although sometimes of a longitudinal figure, 

 and that the divisions of the membrane which forms 

 them, are common to contiguous cells. He further 

 asserts, that these cells communicate with each other by 

 means of pores and slits, about the three hundredth part 

 of a line in diameter ; and that through these perfora- 

 tions the vegetable juices they contain, are slowly trans- 

 ferred. 



