412 VEGETABLE PHYSIOLOGY 
development of the protoplasts of the colony as well as of 
the appearance of new colonies or so-called individuals. 
Indeed in the case of unicellular plants such production 
of new protoplasts is the only form of reproduction 
possible. 
It is important, however, to bear in mind the different 
individualities of the protoplast and of the colony of which 
itis part. Ina filament of Ulothrix or other thread-like 
alga, each protoplast being like every other in all essential 
points, we may regard the formation of new protoplasts in 
the chain as a process of reproduction of the units; as the 
chain, however, grows by means of such multiplication of 
its constituent protoplasts, and has a distinct individuality 
as a filament, we may also regard the process of multiplica- 
tion of the units as one of growth in the length of the 
chain. What is reproduction of the units of construction, 
the protoplasts, is growth of the individual, the colony. 
The same thing is seen in all plants which consist of more 
than a single cell. , 
We may study the method of multiplication of the 
protoplasts either in the cases in which they have an 
independent existence or in those in which each is part of 
a colony. In any case the process involves the division of 
the protoplast into two or many parts, each of which 
strictly resembles in all respects its progenitor. The cases 
in which two new protoplasts result from the fission are 
the most numerous, and they are classed together gene- 
rally under the term cell-division. Of this there are 
various degrees of simplicity ; the most primitive is illus- 
trated by the behaviour of some of the lower fungi, such 
as the Saccharomycetes or yeasts. Each cell, which is 
rounded in form, puts out a lateral protuberance of small 
size, which grows until it is of nearly the same dimensions 
as the one from which it sprang, and is gradually cut off 
by the constriction of the cell-walls at the point of out- 
growth. The new cell or protoplast becomes thus separated 
from its parent, which it resembles in all respects.. This 
