The Plant Cell 



25 



is capable of changing its form or of undergoing differen- 

 tiation when in a position where this response is called 

 forth. It must be un- 

 derstood that this dif- 

 ferentiation is in direct 

 or indirect response to 

 a variety of stimuli 

 w h i c h are normally 

 operative during the 

 growth of the plant. 

 It is found, therefore, 

 that while all the cells 

 of higher plants have 

 developed from an 

 original meristem of 

 the type indicated, 

 there is the greatest 

 diversity in the ulti- 

 mate form, as also in 

 the ultimate work, of 

 the cells differentiated 

 therefrom. 



The different types 

 are, of course, associ- 

 ated with a specialized 

 form of labor, or func- 

 tion ; therefore these cell-types are of peculiar physio- 

 logical importance, as well as of obvious anatomical and 

 evolutionary interest. The following common types may 

 be briefly characterized for further reference : - 



18. Parenchyma. - This type includes various forms 



FIG. 4. Cell from a leaf-hair of squash, 

 showing vacuolate cytoplasm, nucleus, 

 and chloroplasts. 



