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 

 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 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 



