62 HOLISM AND EVOLUTION chap. 



and see what light it throws on the nature and concept 

 of life. 



A few introductory words in regard to the history of our 

 knowledge of the cell may not be out of place here. It will 

 be seen that accurate information even of what little we do 

 know about the cell is of very recent date, and that we are 

 only at the beginning of what may yet prove a great story. 



In the second half of the seventeenth century Robert 

 Hooke observed with the crude microscope then in use that 

 cork and other vegetable substances had a vesicular appear- 

 ance and he called the apparent cavities '' cells." A few 

 years later Grew and Malpighi independently observed in 

 plant tissues these same cavities filled with fluid and sur- 

 rounded with firm walls, as well as what appeared to them to 

 be tubes likewise with walls and filled with fluid. Towards 

 the end of the eighteenth century Treviranus showed that 

 these tubes were cells placed in a row and elongated in the 

 direction of the row and with the partitions between them 

 lost. Then followed in 1831 Robert Brown's great discovery 

 of the nucleus in the cell in plants, and in 1838 Schleiden's 

 elucidation of the great part which the cell with its nucleus 

 plays in the structure of plants, and shortly afterwards the 

 application by Schwann of the new knowledge of the cell to 

 the structure of animals also. Both Schleiden and Schwann 

 attached great importance to the cell wall and looked upon 

 the cells as having crystallised out of some mother substance. 

 The contents of the cells Schleiden called vaguely " vegetable 

 slime "; and it was not till about the middle of the nine- 

 teenth century that the great German biologist von Mohl 

 correctly explained the contents of both vegetable and 

 animal cells as nucleated masses of what he called '' proto- 

 plasm," which was not a chemical crystallisation from other 

 substances, but always came into being as the offspring or 

 daughter cells from other pre-existing cells. Hence arose the 

 formula: omnis cellula e cellula. This paved the way to the 

 correct understanding of sexual fertilisation as the union of 

 two cells, the discovery of cell-divisions, and the part played 

 by the nucleus with its chromosomes in these divisions, and 



