70 



toplasm like grains of sand in a stream. If the living cell 

 examined is in a part of the plant exposed to the light, such 

 as a leaf, it will be found to contain, in addition to the. nucleus 

 and cytoplasm, the so-called chlorophyll corpuscles. These 

 are green bodies, generally ellipsoidal in shape, consisting 

 of dense protoplasm and which owe their colour to the green 

 pigment called chlorophyll which they contain. This pigment 

 is soluble in alcohol and if leaves are boiled and placed 

 in alcohol the green colour can be extracted in the 

 form of a solution. These chlorophyll corpuscles possess the 

 power of making starch from water and the carbon dioxide 

 of the air under the influence of light. The small starch grains, 

 when formed, are dissolved and go to feed the protoplasm, 

 or to be accumulated and stored in certain cells as reserve 

 food material until wanted. In parts of plants not exposed 

 to light, protoplasmic corpuscles essentially similar to the 

 chlorophyll corpuscles are^formed but without the characteris- 

 tic green pigment and sometimes, as in flowers and fruits, the 

 green pigment is replaced by a red, or yellow, one. 



The living contents of the cell thus comprise : 



The Nucleus 

 Cytoplasm 

 Chlorophyll Corpuscles 



for all of which, collectively, the general term, protoplasm is 

 commonly employed. Among the non-living substances fre- 

 quently found in living cells the most important are : 



Starch grains. Large grains are only found in cells where 

 a store of reserve starch is being accumulated. Such grains 

 usually exhibit a distinct stratification, their substance being- 

 arranged in layers. They turn blue when treated with a 

 solution of iodine. 



Alcurene or Proteid grains, These consist chiefly of albu- 

 minous substances and turn yellow-brown when treated with 

 a solution of iodine. They frequently contain albumen crystals 

 which can be distinguished from crystals of inorganic sub- 

 stances by the fact that they absorb stains and swell when 

 treated with water. They also usually contain rounded, or crys- 

 talline, masses of mineral matter. They are common in seeds. 



Albuminous substances are the most complex bodies 

 found in the plant, with the exception of the living proto- 

 plasm itself, and they contain carbon, oxygen, hydrogen,, 

 nitrogen, sulphur, and phosphorus. 



