112 



PLANTS, THE FOOD OF ANIMALS 



mental cells, all firmly attached and forming a tough and re- 

 sisting framework or skeleton giving strength and rigidity 

 to the whole. These woody masses are together called the 

 stereome. Finally there are smaller and more or less circular 

 patches of cells with thick cellulose walls which form the most 

 important organs of the rhizome, the aggregates being termed 

 fibro-vascular bundles. 



If we examine a vertical or horizontal section of the rhizome 

 (Fig. 45) we find that these internal masses of stereome and the 

 fibro-vascular bundles are composed of elongate cellular struc- 



p.s. s.t. 



fp. b. s Y I ZP- 



FIG. 45. Longitudinal section of a fibro-vascular bundle showing the conducting 

 system of the plant in lengthwise section. (From Sedgwick and Wilson). 



tures firmly attached end to end so that continuous supporting 

 structures and tubes traverse the rhizome from end to end, the 

 former serving as an internal skeleton, the latter as conducting 

 and feeding organs. 



At the growing tip of the rhizome the cells are all alike and of 

 the fundamental parenchyma type termed the meristem, but 

 they become differentiated at a short distance from the apical 

 cell and are metamorphosed into cells of varying structure and 

 function, some becoming fibro-vascular cells, others transformed 

 into lifeless stereome. 



These various groups of cells, tubes, supporting structures, 

 etc., are not only continuous throughout the main trunk of the 



