THE CELL. 93 
fore, really seem most proper to provide this chapter with an 
introduction to the construction and use of the microscope. 
There have recently appeared, however, so many publications 
relating precisely to this subject,’ that we may omit further ref- 
erence to it in this place. 
The experience acquired at the preparation table is in the 
end the most important of all ; and as chemical analysis cannot 
be learned without a laboratory, so also the methods of micro- 
scopical investigation cannot be learned without a microscope 
‘and dissecting needles. 
I. The Cell. 
~The elementary organs from which the body of the plant is 
constructed are the cells. Although it is not necessary for the 
. formation of the idea of a cell that the same should be inclosed 
by a membrane (naked swarm-pores), nevertheless, by far most 
cells are provided with such. 
Most plants (all the more highly organized ones) consist of 
numerous cells. Among the lower plants there are, however, 
many which are formed of but single cells, some of which assume 
the most manifold forms, branch abundantly (the mould fungus 
Mucor Mucedo), and, indeed, without being in any manner 
divided by lateral walls, imitate a stem, leaf, and root ( Caulerpa). 
Of such one-celled plants, there are none which come under 
consideration in pharmacognosy in a restricted sense, although 
the yeast fungus (Saccharomyces cerevisiw), on account of its 
fermentative action, and the various pathogenic fungi (dacteria), 
which claim an increased degree of interest in consequence of 
the recently observed relations between them and the most dan- — 
gerous diseases, as well as the Diatomezx, whose siliceous coats 
1 Behrens, ‘‘ Hilfsbuch zur Ausfiihrung mikroskopischer Untersuch- 
ungen,” Braunschweig, 1883. The American edition of this work has 
been noticed on page 49, F. B. P.—Dippel, ‘‘ Das Mikroskop,” II., Braun- 
schweig, 1883-84.—For the theoretical part, the following is very valua- — 
ble: Nageli and Schwendener, ‘‘Das Mikroskop,” Leipzig, 1877.— 
Further: Hager, ‘‘Das Mikroskop und seine Anwendung,” Berlin, — 
1879.—J. Vogel, ‘‘Das Mikroskop,” Leipzig, 1885. . 
