6o 4 POPULAR SCIENCE MONTHLY. 



two elaborate treatises on the minute structure of plants, which 

 had been quite independently worked out, the one by Grew, an 

 Englishman, the other by Malpighi, an Italian. But their admi- 

 rable work remained for more than a hundred years the standard 

 of knowledge in plant anatomy, while the overwhelming author- 

 ity and example of the Linnsean school reduced botany to the 

 superficial examination of dried fragments, and comprised all 

 needed knowledge of a plant in the determination of its Latin 

 name. 



For the beginnings of our real knowledge of the cell we must, 

 then, leap the chasm of a century and a half to come again upon 

 a period of improvement of the microscope as affording the means 

 for further advance. In this case the important discoveries of 

 Amici, resulting in lens systems in which both chromatic and 

 spherical aberration were largely corrected, offered to histologists 

 far better tools than had hitherto been at their command. Grew 

 and Malpighi had distinguished in plants two kinds of elements, 

 approximately isodiametric cells and much elongated vessels ; but 

 Treviranus had shown, early in the present century, that vessels 

 are derived from rows of cells by the obliteration of intervening 

 walls. And about the same time he had rediscovered the now 

 familiar circulation in the gigantic cells of the brittleworts, or 

 Characecz, which, first described in 1772 by Corti, had been for- 

 gotten in the zeal for taxonomy which possessed his contempo- 

 raries. But gradually the idea grew that the contents within the 

 walls of the cell are of importance ; that the real cell is a living 

 thing which nourishes itself and grows. One of the earliest clear 

 expressions of this idea was written by Meyen in 1830, who spoke 

 of cells of higher plants as " little plantlets in the greater." But 

 the general spread of such views and general interest in cell prob- 

 lems date from the time when Schleiden's clear mind was turned 

 upon them. Going directly to the heart of the whole matter as it 

 then stood, he asked, " How do cells arise ? " and set himself to 

 answer the question. As a probable clew to its solution he 

 seized, by a happy inspiration, upon the discovery made a few 

 years before by Robert Brown that the cells of certain plants 

 studied by him contained each a rounded, rather highly refractive 

 body, which he had called, and which is still called, the nucleus. 

 Demonstrating, with the aid of others, the very general occur- 

 rence of this structure in plant cells, Schleiden made it the center 

 of his theories of cell life and cell formation. It is true that his 

 belief that new nuclei are formed by a sort of crystallization out 

 of a mother-liquor and then form centers for the formation of 

 new cells, has been proved to be incorrect. And it is equally true 

 that his idea of the cell as a closed chamber filled with fluid, 

 whose wall is its most essential part, is no longer entertained. 



