178 PLANT BIOCHEMISTRY 



as well as a reservoir lor water recjuired tor osmotic regulation ot the 

 cell. 



Protoplasm 



The protoplasm of the cell contains essentially all the biological 

 catalysts, the enzymes, that are involved in the complex series of reac- 

 tions which we call life. Protoplasm is differentiated into nucleus and 

 cytoplasm. 



Nucleus. Most cells contain a single nucleus, a spherical or ovoid 

 body which is denser than the surrounding cytoplasm. The body of 

 the nucleus is made up of a dense jelly-like mass of complex chemical 

 composition known as the nuclear gel or karyolymph and the chro- 

 matin. Chromosomes, the deoxyribonucleic acid-rich components re- 

 sponsible for hereditary direction in the organism, appear to originate 

 from the chromatin. In only a few cases is it possible to see chromo- 

 somes in the non-dividing nucleus, so it is difficult to make definite 

 statements as to the chromatin-chromosome relationship. Current 

 thought is that during the interphase (interval between cell division) 

 the chromosomes exist in an extended swollen state, filling the whole 

 nucleus evenly. Chemically chromatin is composed of deoxyribo- 

 nucleic acid associated with histone and non-histone protein. The 

 enzymatic activity associated with the nucleus is not well defined at the 

 present time. In addition to chromatin, many cells contain one or 

 more nucleoli. Although the function of the nucleolus is not definitely 

 established, the suggestion has been made that these ribonucleic acid- 

 rich bodies are synthesized in the nucleus and are infiltrated through 

 the nuclear membrane into the cytoplasm. There they function in 

 biological syntheses. 



Cytoplasm. The cytoplasmic portion of the cell is less dense than 

 the nucleus. It is not a homogeneous entity but rather consists of a 

 fluid portion containing suspended particulate matter. A detailed 

 description of all the types of formed matter found in the cytoplasm 

 is not within the scope of this book. However, a brief discussion of 

 certain of them is pertinent. 



The palisade cells and spongy parenchyma (see Figure 8-1) of 

 higher plants contain green-colored, spherical, ovoid, or disc-shaped 

 bodies, 3 to 10 ;a in diameter and 1 to 2 /x in thickness, called chloro- 

 plasts. The number and size of these bodies vary with the species of 

 the plant and the conditions under which the plant is grown. The 

 chlorophyll appears to be concentrated in bodies known as grana 

 which are embedded in a colorless plasma or stroma. In composition 

 the grana are largely protein, lipide, chlorophyll, carotenoid, and 



