Page:An introduction to physiological and systematical botany (1st edition).djvu/44

 14 foundations physiologists have at their pleasure, constructed various theories, relative to the motion of the sap, respiration and other functions, presumed to be analogous to those of animals. The anatomical observations of Mirbel go further than those of Grew, &c., and it is necessary to give a short account of his discoveries.

He finds, by the help of the highest magnifying powers, that the vegetable body is a continued mass of tubes and cells; the former extended indefinitely, the latter frequently and regularly interrupted by transverse partitions. These partitions being ranged alternately in the corresponding cells, and each cell increasing somewhat in diameter after its first formation, except where restrained by the transverse partitions, seems to account for their hexagonal figure. See Tab. I. f. a. The membranous sides of all these cells and tubes are very thin, more or less transparent, often porous, variously perforated or torn. Of the tubes, some are without any lateral perforations, f. b, at least for a considerable