8 A TEXTBOOK OF BOTANY [Ch. II 



absorb the water and mineral salts needed by the plant, to 

 which they give also a firm anchorage in the ground. The 

 showy and complicated flowers effect fertilization, which 

 is requisite in all sexual reproduction. Fruits, whether 

 dry like pods, or edible like berries, are concerned with the 

 formation and dissemination of seeds. The compact hard- 

 coated seeds, containing each an embryo plant and food 

 supply, separating from the parent plant, and remaining for 

 a time dormant, provide a transportable stage whereby 

 plants are spread. Thus each of the six primary parts per- 

 forms a definite function in the economy of the plant as a 

 whole, and each part is therefore, from the physiological 

 point of view, an organ. In addition each of these organs 

 performs functions connected with its own individual ex- 

 istence, notably growth, respiration, and self-adjust- 

 ment to the surroundings. 



The external form of these primary parts, visible to the 

 unaided eye, is correlated with a definite internal anatomy, 

 revealed by thin sections viewed through magnifying lenses. 

 Thus studied, the parts are found composed of definite and 

 symmetrically arranged differentiations of structure called 

 tissues, having each its distinctive position, color, and 

 texture, and each performing a definite part of the organ's 

 function. Thus the veins and green pulp are tissues of the 

 leaf, as are bark, wood, and pith of the stem, though some 

 of the latter are further divisible. These tissues in turn, 

 when viewed by the compound microscope, are found wholly 

 composed of very small structures called cells, which ap- 

 pear as compartments separated by firm walls and holding 

 various contents. Of these contents the most important is 

 the protoplasm, a mobile, gelatinous material, the seeming 

 simplicity of which is belied by its many remarkable prop- 

 erties. It is really the protoplasm which performs the 

 functions of the plant, and which builds the cells, and there- 

 fore the tissues and organs, suited in structure to the work 

 which is done by the respective parts. 



