VI] SAP-VACUOLES, ETC. 75 



found that we have a cell-wall enclosing protoplasm, 

 and this protoplasm comprises a granular and fibril- 

 lated cytoplasm enclosing a nucleus with its nucleolus 

 and other bodies, the principal difference being that in 

 animal cells the cell- wall is not usually a prominent 

 feature. 



Even in vegetable cells the student must not assume 

 that all the organs of the protoplasm are always present 

 in the complete form described. Many cells do not show 

 the plastids, though that is probably in some cases be- 

 cause they are so minute as to be hidden among the 

 granules of the cytoplasm. 



Still more frequently e.g. all Bacteria and Fungi, 

 parasitic plants and the non-green parts of other plants 

 chlorophyll-corpuscles are not seen ; while in a few cases 

 (becoming fewer, however, each year as improved methods 

 of observation are invented and applied) the nucleus 

 seems to be absent, probably because the nuclear matter 

 is not brought together in the form of a definite organ, 

 but remains scattered in the cytoplasm. 



There are two other points to be considered, moreover, 

 before our ideas of the cell are brought into accord with 

 the teachings of modern botany. 



Turning to the embryonic cell described above we 

 notice that its cell-wall is extremely thin, and that its 

 protoplasmic contents completely fill the cavity. 



As this cell gets older we find two events of primary 

 importance happening. 



The first is that minute drops of watery liquid gradu- 

 ally appear in the cytoplasm of the growing cell, and grow 

 larger and larger until they occupy more space than the 

 whole of the rest of the contents. These spherical drops 

 are called Vacuoles, a name given at a time when, owing 

 to their clear appearance the spheres were thought to be 



