REPRODUCTION 421 
of which each consists. In dealing with reproduction, however, 
in the broad sense we must consider also the 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 proto- 
plasts 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 
it is part. In a 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 
ag 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 proto- 
plasts, 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 cages in which they have an inde- 
pendent existence or in those in which each is part of a 
colony. In any case the process mvolves 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 illustrated by 
the behaviour of some of the lower fungi, such as the Sac- 
charomycetes or yeasts. Hach cell, which is rounded in 
form, puts out a lateral protuberance of small size, which 
grows until it ig of nearly the same dimensions as the one 
from which it sprang, and is gradually cut off by the con- 
striction of the cell-walls at the point of out-growth. Part of 
the nucleus passes into the new cell, which becomes thus 
separated from its parent, resembling it, however, in all 
