108 HISTOLOGICAL BOTANY. 



cell ; the whole or a portion of the protoplasmic contents of 

 a mother cell may become one or more new cells ; or the 

 protoplasmic contents of two or more cells may coalesce to 

 form a new cell. 



The formation of cells as in the first case is termed the 

 G ell-division ; as in the second case, the Interior Cell-forma- 

 tion ; and as in the last, the Conjugation. The develop- 

 ment of vegetative organs is accomplished by cell-division ; 

 pollen-grains, spores of the Nokishinobu, Shishigashira, 

 etc. are produced by interior cell-formation ; and spores of 

 Spirogyra, Zygnema, etc. are formed by conjugation. 



Formation of cells 



Cell-division. 



Interior Cell-formation. 



Conjugation. 



SUMMARY. 



Cells are the elementary organs of plants and are usually more or less 

 .sac-like. 



The cell-wall is the outer membrane of a cell and consists of cellulose, 

 water, and ash-constituents. 



The sieve markings of a cell-wall are those which are produced by true 

 perforations. 



The pitted markings of a cell-wall are those which are produced by 

 numerous canals opening at one end. 



The bordered pits of a. cell-wall are those markings which are produced 

 by hemispherical canals opening at the apex. 



The scalariform markings of a cell-wall are those which are produced by 

 transverse narrow canals closely disposed one above another. 



The annular markings of a cell- wall are those which are produced by ring- 

 like interior prominences. 



The spiral markings of a cell-wall are those which are produced by 

 spiral-shaped interior prominenoes. 



The reticulated markings of a cell-wall are those which are produced by 

 net-like interior prominences. 



The cuticularized cell-wall is one which is so modified that it is extensible, 

 highly elastic, and almost impermeable to water. 



