Vague Foreshadowings of the Cell-Theory.—In attempting to trace the growth of this idea, as based on actual observations, we first encounter vague foreshadowings of it in the seventeenth and the eighteenth centuries. The cells were seen and sketched by many early observers, but were not understood.
As long ago as 1665 Robert Hooke, the great English microscopist, observed the cellular construction of cork, and described it as made up of "little boxes or cells distinguished from one another." He made sketches of the appearance of this plant tissue; and, inasmuch as the drawings of Hooke are the earliest ones made of cells, they possess especial interest and consequently are reproduced here. Fig. 72, taken from the Micrographia, shows this earliest drawing of Hooke. He made thin sections with a sharp penknife; "and upon examination they were found to be all cellular or porous in the manner of a honeycomb, but not so regular."
Fig. 72.—The Earliest Known Picture of Cells from Hooke's Micrographia (1665). From the edition of 1780.
We must not completely overlook the fact that Aristotle (384-322 B.C.) and Galen (130-200 A.D.), those profound thinkers on anatomical structure, had reached the theoretical position "that animals and plants, complex as they may appear, are yet composed of comparatively few elementary parts, frequently repeated"; but we are not especially concerned with the remote history of the idea, so much as with the principal steps in its development after the beginning of microscopical observations.
Fig. 73.—Sketch from Malpighi's Treatise on the Anatomy of Plants (1670).