70 PHARMACEUTICAL BOTANY 



They are only evident after properly fixing and staining cells con- 

 taining them. 



Chloroplastids are plastids found in cells exposed to light and con- 

 tain the green pigment, chlorophyll. 



Chromoplastids are plastids found in cells independent of their 

 relation to light or darkness and contain a yellow, orange or red 

 pigment called chromophyll. 



CELL FORMATION AND REPRODUCTION 



The cells of plants have all been derived from preexisting cells. 

 In the bacteria and many other low forms of plant life, the division 

 of the cell always results in reproduction; in higher forms, however, 

 it merely increases the size of the individual and so is a phenomenon 

 of growth. 



There are two kinds of cells formed by plants, viz. : asexual and 

 sexual. Both of these are endowed with the possibilities of repro- 

 duction, although the former are frequently limited to the process 

 of growth. 



Reproduction is the power possessed by an organism of giving rise 

 to new individuals. This may take place through the agency of 

 either asexual or sexual cells and is accordingly asexual or sexual in 

 character. Whenever a union of cells or their protoplasmic con- 

 tents takes place the process is called " sexual reproduction;" if, 

 however, there is a mere separation of a cell or cells from an indi- 

 vidual which later form a new organism, the process is termed 

 " asexual or vegetative reproduction." 



There are four modes of asexual reproduction, viz.: Fission, 

 Gemmation, Free Cell Formation and Rejuvenescence. 



Fission. This is the separation of a cell into two equal halves, 

 each of which may grow to the size of the original parent cell from 

 which it was derived. Fission is seen in the reproduction of bac- 

 teria, growth of many algae and the formation of tissues of higher 

 plants. 



Gemmation or Budding. This is the method of reproduction 

 common among yeasts. The cell forms a protuberance called a 

 bud which increases in size until it equals the size of the cell which 

 formed it and then becomes detached, although frequently not until 

 it has developed other buds and these still others. 



