The Plant Cell 



29 



bundles, and are easily identified in the outer part of 

 these (commonly in the hark, therefore, of dicotyledonous 

 plants). They are regarded as most important in the 

 conduction of the less diffusible organic materials. 



The arrangement or association of certain of these types 

 of cells and further indications respecting their several 

 functions in the general physiology of the plant are again 

 referred to under growth and transport. 



FIG. 6. Conducting cells of fibrovascular bundles, ducts, tracheae (I) ; 

 pitted vessel (rri) sieve tubes with companion cells, in longitudinal (ri) 

 and cross section (o). [Adapted.] 



23. Protoplasmic movement. - - Naked protoplasmic 

 units or aggregates such as amoebae, or the plasmodia of 

 Myxomycetes, show a considerable power of locomotion 

 due to streaming movements in the cytoplasm. It is 

 also well established that within the protoplast of a variety 

 of cells invested with a firm cell-wall there is relatively 



