8 THE STORY OF PLANT LIFE 



required. The protoplasts also help in the work of 

 respiration when by katabolism their substance is 

 transformed into simpler materials. 



The nucleus is usually spherical and central or 

 right-handed, and consists of a nuclear membrane, 

 nuclear reticulum, and nuclear sap, with nucleoli. 

 The first is a membrane like the ectoplasm. The 

 reticulum is akin to the cytoplasm. The nuclear 

 sap is a fluid which affords food and water, and the 

 nucleoli contain reserves for nuclear- and cell-division. 

 The nucleus is the portion of the cell which trans- 

 mits the hereditary characters, and has to do mainly 

 with reproduction and more or less all cell division. 

 If it is damaged the plant dies. 



In the protoplast are small bodies called plastids, 

 which are round or of various shapes. The colourless 

 ones are leucoplasts. The green ones are chloro- 

 plasts, the yellow orange or red ones are chromo- 

 plasts. One type may develop into the other, but 

 each performs a different function. The leucoplasts 

 give rise to the other types and make the starch- 

 grains out of the soluble carbohydrates. The 

 chloroplasts secrete chlorophyll - green and chloro- 

 phyll-yellow, and by means of these pigments the 

 sun's energy is utilised to turn the carbon dioxide 

 in the atmosphere into carbon, which is elaborated 

 later into starch within the cell-sap. By aid of the 

 chromoplasts the red, orange and yellow colours of 

 flowers and fruits are obtained. Blue and red colours 

 are formed also by anthocyan. 



