THE PLANT-CELL 35 



condition by the access of water. Other familiar examples of dor- 

 mant protoplasm are offered by the spores of the lower plants and 

 the seeds, bulbs, tubers, etc., of many of the Flowering Plants. 



Where the protoplasm is free from secondary pigments it appears, 

 iu mass, more or less whitish or milky from the numerous granules 

 imbedded in its transparent ground substance. These granules are 

 evident as soon as it is sufficiently magnified. The protoplasm then 

 shows an apparently homogeneous colorless ground substance (Hya- 

 loplasm), in which are imbedded many granular bodies of different 

 sizes. The larger granules are usually not essential parts of the 

 protoplasm, being either food bodies taken from without, or else 

 products of the activity of the protoplasm itself, like starch granules 

 and albuminous granules. There are, however, numerous extremely 

 minute granules (Microsomes), which give the protoplasm a finely 

 punctate appearance, and which are usually considered to be inte- 

 gral parts of its substance. The protoplasmic mass is always 

 bounded by a more or less evident layer of hyaloplasm, and a simi- 

 lar layer lines the vacuoles, or spaces filled with fluid, which occui- 

 within the protoplast. The outer hyaloplasm is less fluid than the 

 inner granular plasma, and is much less motile. Where the proto- 

 plasm is included within a cell-wall, the hyaloplasm forms a contin- 

 uous layer between the cell-wall and the granular portion of the 

 protoplasm. 



Differentiation of the Protoplast 



While the term Protoplasm is used for the whole living contents 

 of the cell, it must be remembered that these are by no means homo- 

 geneous, and in all but the lowest organisms there is an evident dif- 

 ferentiation of the protoplast, or living cell-body, into definite parts, 

 which are essential elements of the cell, and capable of being in- 

 creased only by division of similar parts. These special parts are 

 the Cytoplasm, Nucleus, and Plastids or Chromatophores. Of more 

 doubtful nature are the Centrosomes and Tonoplasts, which have 

 been also considered to be permanent constituents of the cell. 



Cytoplasm The main body of the protoplast, in which the other 

 protoplasmic structures are imbedded, is known as Cytoplasm, which 

 is not infrequently called simply protoplasm in distinction from the 

 Plastids and Nucleoplasm (Karyoplasm). The cytoplasm always 

 shows an apparently homogeneous ground substance, or hyaloplasm, 

 in which are imbedded the microsomes and other granular bodies 

 which are present. The granules are confined to the inner, more 

 fluid portions, while the layer bounding the outside of the proto- 

 plast, and the inner part surrounding the sap-cavities, or vacuoles, 

 are firmer and quite homogeneous. The larger granules are of 

 various kinds, starch, aleurone, crystals, etc. Sometimes the ap- 



