The Cal as an Individual. a6 
Actually to observe this, it is necessary to add to the cells at 
‘the proper stages some substance with an attraction for water, 
such as alcohol, so as to contract the protoplasmic con- 
tents (Fig. 56). Examples of this are furnished by many 
— filamentous Algze, as well as m the formation of the pollen- 
grains of many Dicotyledons. The formation of the new 
cell-wall does not always proceed so gradually and uniformly 
along with the division of the protoplasm; in many cases, as 
in the formation of the pollen-grains of the great majority of 
Monocotyledons, the production of the entire cell-wall takes 
place suddenly, or at least so rapidly that it is impossible to 
detect the intermediate steps (see Fig. 55 I., p. 33). The 
number of daughter-cells which arise in the mother-cell — 
- yaries, but is always uniform in any particular case. 3 
Not only is the number of cells increased by cell-multi- 
plication, but, in consequence of the newly-formed cells re-_ 
taining a connection with one another, the possibility is 
afforded of the production of larger cellular structures, the 
most complete development of which occurs in the higher 
_ plants. 
CHAPTER, 1. | 
THE CELL AS A MEMBER OF A GROUP OF SIMILAR CELLS. 
ONLY a comparatively small number of plants consist, during 
the whole period of their existence, of a single cell; in the 
greater number the cells are united into groups. The pro- 
duction of these groups of cells is caused by two circum- 
stances :—In the first place, the cell-walls of young con-- 
tiguous cells, where they are in contact with one another, 
amalgamate into a homogeneous mass; and secondly, cells 
- originally distinct coalesce with one another when the 
portions of the walls that are in contact are of nearly the 
same nature. This union of adjacent cells is so intimate 
D.i2 
