60 THE MECHANICAL FUNCTIONS. 



or oval perforations, as shown in Fig. 10. Cells of 

 this description are said to be reticulated or spotted, 

 and these, together with cells having more regularly 

 formed spiral threads, are very abundantly met 

 with in plants belonging to the tribe of OvchidecB. 



It has been much disputed whether the cells of 

 the vegetable texture are closed on all sides, or 

 whether they communicate with one another. 

 Mirbel has given us delineations of what appeared 

 to him, wlien he examined the coats of the cells 

 with the microscope, to be pores and fissures. But 

 subsequent observations have rendered it probable 

 that these appearances arise merely from darker 

 portions of the membranes, where opaque particles 

 have been deposited in their substance. Fluids 

 gain access into these cells by transuding through 

 the membranes which form their sides, and not by 

 any apertures capable of being detected by the 

 highest powers of the microscope. 



If all the cells consist of separate vesicles, as the 

 concurring observations of modern botanists* ap- 

 pear to have satisfactorily established, the partitions 

 which separate them, however thin and delicate, 

 must consist of a double membrane, formed by the 

 adhesion of the coats of the two contiguous vesicles. 

 But as these coats can hardly be supposed to adhere 

 in every point, we may expect to find that spaces 

 are left in various parts between them ; and that 

 communications exist to a certain extent between 

 all these spaces ; so as to compose what may be 

 regarded as one large cavity. These have been 

 denominated the intercellular spaces; and they have 



* 111 particular, Treviranus, Kieser, Link, Dii Petit Thouars, Pol- 

 lini, Ainici, Duliochct, and De Candrllc. 



