THE STRLCrURAL (JOMFONENTS OF RROTOl'LAST.S 



3: 



static pressure. The movement of the gametes in Spirogyra is (lep(>ndent 

 in part upon the activity of such vacuoles. 



In the meristematic cells of plants the vacuoles are usually much 

 smaller and more numerous than in differentiated cells. As the cells 



Fm. 25. — Cell from onion root, showing Fig. 26. — Various forms assumed by 



vacuoles. vacuoles in fusiform cambium cells of 



locust tree. (After I. W. Bailey.) 



derived from the meristem enlarge, multiply, and differentiate, their 

 vacuoles increase in size, undergo internal chemical changes, and gradu- 

 ally unite, thus forming one or more vacuoles of large size (Fig. 27). 

 Often vacuoles in living cells can be seen to become fragmented as a 



Fig. 27. — Vacuoles (stippled) a-d, successive stages in bud of a conifer (Abies); e, pollen 

 grain of a conifer (Cephaloiaxus). (After P. Dangeard.) 



result of protoplasmic streaming; also at the time of cell division they 

 may be passively divided. 



The origin of the small vacuoles in the meristem has been variously 

 conceived. It was at one time thought that the cytoplasm contained 

 individualized bodies (tonoplasts) derived only from previous ones by 



