THE HISTORY OF THE CELL-THEORY 3 



The study of the lowest plants has also proved of the greatest 

 importance in establishing the cell-theory. Small alga? were 

 observed, which during their whole lifetime remain either single 

 cells, or consist of simple rows of cells, easily to be separated 

 from one another. Finally, the study of the metabolism of plants 

 led investigators to believe that, in the economy of the plant, it is 

 the cell which absorbs the nutrient substances, elaborates them, 

 and gives them up in an altered form (Turpin, Raspail). 



Thus, at the beginning of our century, the cell was recognised 

 by many investigators as the morphological and physiological 

 elementary unit of the plant. This view is especially clearly 

 expressed in the following sentences, quoted from the Text-hook of 

 Botany (I. 16), published by Meyen in 1830: " Plant-cells appear 

 either singly, so that each one forms a single individual, as in the 

 case of some alga? and fungi, or they are united together in greater 

 or smaller masses, to constitute a more highly-organized plant. 

 Even in this case each cell forms an independent, isolated whole ; 

 it nourishes itself, it builds itself up, and elaborates the raw 

 nutrient materials, which it takes up, into very different sub- 

 stances and structures." In consequence, Meyen describes the 

 single cells as " little plants inside larger ones." 



These views, however, only obtained general acceptance after the 

 year 1838, when M. Schleiden (I. 28), who is so frequently cited 

 as the founder of the cell-theory, published in Muller's Archives 

 his famous paper " Beitrage zur Phytogenesis." In this paper 

 Schleiden endeavoured to explain the mystery of cell-formation. 

 He thought he had found the key to the difficulty, in the discovery 

 of the English botanist, R. Brown (I. 5), who, in the year 1833, 

 whilst making investigations upon orchids, discovered nuclei. 

 Schleiden made further discoveries in this direction ; he showed 

 that nuclei are present in many plants, and as they are invariably 

 found in young cells, the idea occurred to him, that the nucleus 

 must have a near connection with the mysterious beginning of the 

 cell, and in consequence must be of great importance in its life- 

 history. 



The way in which Schleiden made use of this idea, which was 

 based upon erroneous observations, to build up a theory of phyto- 

 genesis, must now be regarded as a mistake (I. 27) ; on the other 

 hand, it must not be forgotten that his perception of the general 

 importance of the nucleus was correct up to a certain point, and 

 that this one idea has in itself exerted an influence far beyond the 



