1 82 Robe r /son: The Plant Cell. 



the cell, as perhaps it mii^ht be termed, is not confined to the 

 epidermis, beino;- also found, not only in the pubescence of the 

 surface, particularly when jointed, as in Cyprepedium, but in 

 many cases in the parenchyma or internal cells of the tissue .... 

 The nucleus of the cell is not confined to Orchide;c, but is equally 

 manifest in many other Monocotyledonous families ; 1 have even 

 found it, hitherto however, in a very few cases, in the epidermis 

 of Dicotyledonous plants.' 



The most epoch-making- work of this period was Schwann's 

 * Microscopische Untersuchungen,' (1839), which laid the 

 foundations of the cell theory. The keynote to Schwann's 

 remarkable book is found in the sentence ' It may be asserted 

 that there is one universal principle of development for the 

 elementary parts of org-anisms, however different, and that this 

 principle is the formation of cells.' This theor\' is now so 

 completely taken for g^ranted that it is quite difficult to realise 

 that there was a time, not so very long- ag^o, when it was new 

 and revolutionary. The year 1839 may perhaps be reg"arded as 

 the biolog-ical ' annus mirabilis ' of last century, marked as it was 

 by the foundation of the cell theory, and also by the first clear 

 conception by Charles Darwin of the idea of Natural Selection, 



As soon as the truth of the cell theory had been really 

 demonstrated, the question arose — how do the cells of the body 

 orig-inate? Most unluckily Schwann and Schleiden made the 

 mistake of supposing- that cells mig-ht arise in two different ways, 

 either by division of a pre-existing^ cell, or by crystallising-, as it 

 were, out of a formless medium. They thoug-ht the latter 

 process the usual and typical one. Schwann says ' .-\ structure- 

 less substance is present in the first instance, which lies either 

 around or in the interior of cells already existing- ; and cells are 

 formed in it in accordance with certain laws, which cells become 

 developed in various ways into the elementary parts of 

 organisms.' Hugo von Mohl had recognised, as early as 1835, 

 what we now know to be the true view, namely that no cell can 

 arise except from a pre-existing cell by division, but it was not 

 until twenty years later that the pathologist Virchow actually 

 drove it home, and insisted that ' omnis cellula e cellula.' To 

 von Mohl, who in so many ways was ahead of his age, we owe 

 the word ' prot()i)lasni,' which he first used in 1846. After 

 speaking of tin- nucU'us lu- sa\s, 'The remainder of the cell is 

 more or less conipletely filled with an opake, viscid fluid of a 

 white colour, ha\ing granules intermingled with it, which fluid 

 I call pro/op/dsni.' It was Huxley who brought the word 



Naturalist, 



