CHAPTER II. 



CELL-CONTENTS AND CELL-WALLS. 

 I. THE CELL ; NUCLEAR AND CELL DIVISION. 



26. The Vegetable Cell. The body of the higher 

 plants consists of various forms and modifications of 

 cells. A normal uninucleate cell consists of two series 

 of parts : (1) the protoplast, (2) ergastic or secondary 

 structures. 



(1) The protoplast or protoplasm body is again di- 

 visible into (a.) protoplasmatic organs and (b) allo- 

 plastic organs. The former are distinguished by the 

 fact that they do not arise de novo, but are multiplied 

 by division, (a-) To the protoplasmatic bodies belong 

 (i) the cytoplasm, or general protoplasm ; (ii) the 

 nucleus, with the chromosomes ; (iii) the trophoplasts, 

 which are either autoplasts (usually chloroplasts) 

 capable of photosynthesis, or leucoplasts, or chromo- 

 plasts. (b) The alloplastic organs, which arise by slight 

 alteration of the ordinary protoplasm, include (i) the 

 surface layer of the cytoplasm, lying immediately within 

 the cell-wall ; (ii) the tonoplast, or layer lining vacuoles ; 

 (iii) the cilia of motile cells (zoospores, etc.). 



(2) The ergastic structures are formed by the pro- 

 toplasm, cannot multiply by division, and arise de novo as 

 either (a) inclusions of the protoplast e.g. cell-sap, oil 

 drops, calcium oxalate crystals, starch grains, pro- 

 tein crystals, or as (6) excretions of the protoplast 

 e.g. the cell-wall. 



27. Protoplasm, Nucleus, Mitosis, Cell-Division. 



In order to make out the minute details of protoplasmic 

 and especially of nuclear structure, the materials must be 



27 



