KEPKODUCTION 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 

 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 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 cases in which they have an inde- 

 pendent 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 illustrated by 

 the behaviour of some of the lower fungi, such as the Sac- 

 charomycetes 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 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 



