8 PROTOPLASM AND PLANT CELLS 
cells are binucleate while they are uninucleate in the 
remaining stages. In some groups of plants, however, 
we find that, enclosed in an outer cell wall, there is a 
mass of cytoplasm containing many nuclei. Such a 
structure is called a coenocyte. It is frequently re- 
garded as consisting of as many cells as nuclei are present, 
not separated, however, by partition walls. Perhaps it 
may better be considered as a sort of compound cell as 
the nuclei do not seem to control definite masses of cy- 
toplasm. In some coenocytes of the seaweed Griffithsia 
over 4,000 nuclei are present, while in the enormous 
coenocyte of Caulerpa, likewise a seaweed, which often 
attains a length of several decimeters, the number of 
nuclei is vastly greater. Coenocytes are mostly re- 
stricted to certain groups of lower plants, but cells of 
coenocytic nature may occur even in the higher plants. 
17. In shape cells are very variable. Usually we find 
that free-living cells approach the spherical shape al- 
though they are often elongated somewhat. Cells 
united to other cells are usually flattened on the sides 
where they are in contact. When surrounded by cells 
at all sides cells are usually more or less regular, several 
to many-sided polyhedra. Some cells are cylindrical 
while often we have fiber or spindle shaped cells. Some 
cells are lobed or branched. 
Laboratory Studies. It is assumed that the attempt will 
not be made to use this book without endeavoring to carry 
out in the laboratory all or at least a selection of the laboratory 
exercises suggested here and there in connection with the 
various topics. So far as possible the suggested exercises 
have been made simple enough for the student to undertake 
himself, depending as little as possible upon specimens prepared 
or experiments set up by the teacher. It is absolutely essential 
that each student have the use of a good compound micro- 
scope, and that he possess the proper tools for making sections, 
