228 PLANT STUDIES 
nucleus lies imbedded within it (Fig. 200). Every working 
cell consists of at least cytoplasm and nucleus. Sometimes 
the cellulose wall is absent, and the cell then consists sim- 
ply of a nucleus with more or less cytoplasm organized 
about it, and is said to be naked. 
Another protoplasmic organ of the cell, very conspicuous 
among the Algae and other groups, is the plaztid. Plastids 
are relatively compact bodies, commonly spherical, variable 
in number, and lie imbedded in the cytoplasm. There are 
various kinds of plastids, the most common being the one 
which contains the chlorophyll and hence is stained green. 
The chlorophyll-containing plastid is known as the chloro- 
plastid, or chloroplast (Fig. 200). An ordinary alga-cell, 
therefore, consists of a cell wall, within which the proto- 
plasm is organized into cytoplasm, nucleus, and chloroplasts. 
The bodies of the simplest Algae consist of one such 
cell, and it may be regarded as the simplest form of plant 
body. Starting with such forms, one direction of advance 
in complexity is to organize several such cells into a loose 
row, which resembles a chain (Fig. 202) ; in other forms 
the cells in a row become more compacted and flattened, 
forming a simple filament (Fig. 203) ; in still other forms 
the original filament puts out branches like itself, produc- 
ing a branching filament (Fig. 207). These filamentous 
bodies are very characteristic of the Algae. 
Starting again with the one-celled body, another line of 
advance is for several cells to organize in two directions, 
forming a plate of cells. Still another line of advance is for 
the cells to organize in three directions, forming a mass of 
cells. 
The bodies of Algae, therefore, may be said to be one- 
celled in the simplest forms, and in the most complex forms 
they become filaments, plates, or masses of cells. 
157. Reproduction. In addition to the work of nutrition, 
the plant body must organize for reproduction. Just as the 
nutritive body begins in the lowest forms with a single cell 
