BIOLOGY OF HIGHER SEED PLANTS 



23 



c. Who made the first observations similar to the one 

 you have just made ? What conclusions did he 

 draw concerning the structure of plants ? Consult 

 the text (Chapter IV, p. 54). 



3. High-power study. Observe a portion of the above section 

 under high power, being careful to secure good light. 



B D 



FIG. 8. Cell and tissue differentiation in plant organs 



A, cross section of a root with dark pith, light vascular bundles, and dotted 

 cortex ; B, cross section of flower stalk with tissues as in A but with an outer 

 layer (dark) of thick-walled strengthening collenchyma cells ; C, single-celled alga 

 with nucleus (n) ; I), cross section of a square-stemmed plant (col, collenchyma, 

 as in B ; fv, fibrovascular bundles ; pith and cortex dotted) 



a. Cell ivalls. Note their thickness, color, and connections 

 in adjacent cells. Is the cell wall split at the junc- 

 tion of adjacent cells to leave minute spaces, called 

 intercellular spaces ? 



fi. Cell cavities. Note their size, shape, and , contents. Are 

 the cell cavities of adjacent cells similar in these 

 respects ? Do the cavities of these cells contain 

 anything besides air ? 



