32 PLANT LIFE. 



la addition to the typical form of cell described above, 

 certain modified forms of cell occur, the most remarkable 

 being the primordial or naked cell, so called on account 

 of the entire absence of the cell-wall. Such, cells are only 

 met with in the simplest of the two primary divisions of 

 plants called Cryptogams, and are usually connected with 

 reproduction. The movements of the protoplasm constitut- 

 ing primordial cells are generally much more marked than 

 when enclosed within a cell-wall, and may be conveniently 

 described under two headings. The first is when the whole 

 cell moves rapidly, due to the presence of a varying number 

 of cilia or exceedingly fine hair-like prolongations of the 

 outermost hyaline layer or ectoplasm of the protoplasm. 

 In the second type the movement of the cell depends on 

 its constantly changing form ; a few rather stout prolong- 

 ations of its substance are protruded and then withdrawn, 

 similar prolongations or pseudopodia being protruded from 

 fresh points of the surface of the cell ; the movement, being 

 effected in a similar manner to that of the simple animal 

 organism known as Amoeba, is called amceboid. It will have 

 been observed that in the last described movement the 

 organs of locomotion are temporary, whereas cilia are 

 permanent. 



Light, heat, and free oxygen appear to be indispensable 

 factors in connection with all protoplasmic movements. 



Formation of New Cells. — The origin of new cells always 

 depends on various modifications undergone by previously 

 existing cells, and may be referred to under two headings : 

 {a) Vegetative; (b) Reproductive. 



The vegetative parts of a plant include all structures 

 collectively administering to the well-being of the individual, 

 as root, stem, leaves, etc., and in such parts the almost 



