Cells and Cell Principle 43 



ANIMAL CELLS 



PLANT CELLS 



7. Vacuoles (vak' u ol) (L. vacuus, 

 empty). — Spherical vesicles (ves' i- 

 kal) (L. vesica, bladder) of liquid, 

 and of various sizes, are known as 

 vacuoles and may be present or ab- 

 sent in the cytoplasm of animal 

 cells, A vacuolar membrane sep- 

 arates the vacuole contents from the 

 cytoplasm. Vacuoles may contain 

 materials to be digested and ab- 

 sorbed or wastes to be excreted. 



Vacuoles. — The central region of a 

 plant cell usually contains one or 

 more rather clear vacuoles contain- 

 ing cell sap. The vacuolar mem- 

 brane lines the vacuole. In general, 

 in younger cells the vacuoles are 

 smaller and more numerous, but as 

 the cell grows the smaller vacuoles 

 coalesce and become larger and 

 fewer in number. 



8. Plastids (Or. plastos, to form). — 

 These are special bodies of various 

 sizes and shapes and are capable of 

 forming certain substances. They 

 are common in plant cells but are 

 occasionally present in some of the 

 lower animals. 



8. Plastids. — These are specialized, 

 definitely organized bodies, usually 

 oval or spherical in shape, which 

 may be visible in the living condi- 

 tions. They are of three types: (a) 



* chromoplasts (kro' mo plast) (Or. 

 chroma, color; plastos, moulded) 

 are red, yellow, or organe and are 

 common in flowers, fruits, etc.; (b) 

 leucoplasts (lu'ko plast) (Or. leukos, 

 white) are colorless and occur most 

 commonly in storage cells of roots 

 and underground stems; (c) chlor- 

 oplasts (klor' o plast) (Or. chloros, 

 green) are greenish because of 

 chlorophyll and occur in virtually 

 all green cells where they photo- 

 synthesize foods. 



Metaplasm (Cell Inclusions) (met' a- 

 plazm) (Or. meta, between; plasma, 

 moulded). — This is a lifeless, pas- 

 sive structure of the cytoplasm and 

 includes fat droplets, reserve foods 

 (proteins, glycogen, yolk, etc.), 

 excretory materials, crystals, etc. 



9. Metaplasm '(Cell Inclusions). — This 

 is a lifeless, passive inclusion and 

 includes stored foods (starch, pro- 

 teins, fats), waste materials, crystals, 

 etc. 



II. Nucleus (nu'kleus) (L. 

 kernel, or nucleus) 



nucleus. 



1. Nuclear Membrane. — The thin nu- 

 clear membrane separates the nu- 

 cleus from the cytoplasm and ad- 

 heres closely to the nucleus. 



II. Nucleus 



1. Nuclear Membrane. — The thin, liv- 

 ing membrane separates the nucleus 

 from the cytoplasm. Living plant 

 nuclei are usually rather large, color- 

 less, and viscus and may be spheri- 

 cal, oval, or elongated. 



