THE GENERAL STRUCTURE OF PLANTS 11 



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have a number of protoplasts arranged together over 



the inner surface of a common cell-wall. The separate 



protoplasts are often in such close contact with each other 



that their separate outlines cannot be detected. They 



have the appearance of a mass of protoplasm lining the 



wall of a hollow, generally tubular, 



cavity, and having a large number 



of nuclei embedded in the mass. 



The presence of a number of nuclei 



indicates that there are really as 



many protoplasts, as we have seen 



a nucleus is an essential part of one 



of the latter. Moreover, a single 



protoplast contains only a single 



nucleus. 



The difference between a colony 

 of this kind and one constructed 

 like Chroococcus or Volvox is the 

 absence of a cell-wall between the 

 protoplasts. They are a stage 

 higher than the Myxomycetes, as 

 the whole colony is protected by an 

 external membrane. 



Other co3nocytes exist in which, 

 besides the limiting wall, certain 

 transverse walls exist, dividing up 

 the chamber into compartments. 

 This condition is intermediate 



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ocyte already ae- 

 scribed and the simple colony or 

 the multicellular plant. 



In most cases the division of 



the cells goes on for a considerable time and may continue 

 almost indefinitely, the number of the constituent proto- 

 plasts becoming very great and the colony proportionately 

 large. According to the direction of the divisions we 

 get filaments (fig. 13), plates (fig. 14), or masses of cells, 



FIG. 12. EMBRYO OF Orobus 

 AT THE BASE OF A LONG 

 SUSPENSOR. THE LATTER 

 SHOWS A C03NOCYTIC STRUC- 

 TURE. (After Guignard.) 



