2 INTRODUCTION. 



Wien, 1838, p. 14,) they in like manner consist of cells, the 

 partition- walls of which become obliterated. 



Animals, which present a much greater variety of external 

 form than is found in the vegetable kingdom, exhibit also, and 

 especially the higher classes in the perfectly-developed condition, 

 a much more complex structure in their individual tissues. 

 How broad is the distinction between a muscle and a nerve, 

 between the latter and cellular tissue, (which agrees only in 

 name with that of plants,) or elastic or horny tissue, and so 

 on. When, however, we turn to the history of the development 

 of these tissues, it appears, that all their manifold forms originate 

 likewise only from cells, indeed from cells which are entirely 

 analogous to those of vegetables, and which exhibit the most 

 remarkable accordance with them in some of the vital pheno- 

 mena which they manifest. The design of the present treatise 

 is to prove this by a series of observations. 



It is, however, necessary to give some account of the vital 

 phenomena of vegetable cells. Each cell is, within certain 

 limits, an Individual, an independent Whole. The vital phe- 

 nomena of one are repeated, entirely or in part, in all the rest. 

 These Individuals, however, are not ranged side by side as a 

 mere Aggregate, but so operate together, in a manner unknown 

 to us, as to produce an harmonious Whole. The processes 

 which go forward in the vegetable cells, may be reduced to the 

 following heads : 1, the production of new cells; 2, the expan- 

 sion of existing cells; 3, the transformation of the cell-contents, 

 and the thickening of the cell-wall ; 4, the secretion and ab- 

 sorption carried on by cells. 



The excellent researches of Schleiden, which throw so much 

 light upon this subject, form the principal basis for my more 

 minute observations on these separate vital phenomena. (See his 

 " Beitrage zur Phytogenesis," in Midler's Archiv, 1838, p. 137, 

 plates 3 and 4.)i 



First, of the production of new cells. According to Schleiden, 

 in Phamogamous plants, this process always (except as regards 

 the cells of the Cambium,) takes place within the already ma- 

 ture cells, and in a most remarkable manner from out of the 

 well-known cell-nucleus. On account of the importance of the 



1 [A translation of this paper forms part of this volume. — Trans.] 



