346 Development and [BOOK n. 



tissue of Algae, parenchyma and its cells, vessels of the plant, 

 wood and its cells, bast-cells, stomata, appendicular organs of 

 the epidermis, cork ; then follows a paragraph on the thick- 

 ening-ring, and then to the no small astonishment of the 

 reader comes an account of the vascular bundles, after the 

 vessels, the wood, and the bast-cells have been already dis- 

 missed. That such a mode of presenting the subject is due to 

 the little insight possessed by the writer into the structure of 

 the plant as a whole is apparent from simply reading the book, 

 and a similar confusion of ideas is found in his text-book of 

 1856. 



We find a much better classification of tissues in 1855 in 

 Unger's ' Anatomic und Physiologic der Pflanzen ' ; an account 

 of cells is followed by a description of cell-complexes, as one 

 of the chief divisions of the book, and herein of cell-families, 

 cell-tissues, and cell-fusions. Another chief section is occupied 

 with cell-groups, and here epidermal formations, air-spaces, 

 sap-receptacles, glands and vascular bundles are noticed ; 

 here certainly the fact has been overlooked that vascular 

 bundles may be co-ordinated with epidermal formations, but 

 not air-spaces, sap-receptacles and glands. His last chief 

 division gives an account of tissue-systems and of the way in 

 which the vascular bundles are united together in different 

 plants, and secondary growth in thickness and the activity of 

 the cambium-layer are described quite in the right connection. 



In this branch of the science, as in every case where it is a 

 question of establishing fundamental conceptions, of surveying 

 facts from extensive points of view, and of seeking the requisite 

 principles by means of the history of development, we find that 

 it is Nageli who opens the way and lays the foundation. In 

 his ' Beitrage zur wissenschaftlichen Botanik' of 1858, he pro- 

 posed a classification of tissues from purely morphological 

 points of view. His first division was into generating and 

 permanent tissue ; in each section he distinguished two forms, 

 prosenchymatous and parenchymatous tissue. Parenchymatous 



