CONTENTS OF CELLS. 



497 



presents the appearance of a central cavity or vacuole containing 

 one or more small granules called nucleoli. 



Fig. 547. 



Fig. 548. 



Fig 547. Upper end of a young hair of the stamen of Tradescantia , showing the cells in 



various stages of development ; n, n, nuclei. Magn. 400 diam. 

 Fig. 548. Cell with a nucleus, from the stem of Orchis mascula. Magn. 400 diam. 



The nucleus is not usually found in Fungi or Lichens ; and many Algee 

 are likewise unprovided with it. 



Movements of the Nucleus, &c. The nucleus probably originally 

 occupies the centre of all nascent cells where it exists, the inter- 

 space between it and the primordial utricle being filled up by pro- 

 toplasm. When the vacuolar displacement of the latter by watery 

 cell-sap takes place, the nucleus, if persistent, is usually carried to 

 one side of the cell, and comes into contact with the inner boundary 

 of the primordial utricle. Sometimes, however, it remains sus- 

 pended in the centre of the cell by cords of tough protoplasm, 

 stretched from a layer of protoplasm coating the nucleus to that 

 which lies upon the primordial utricle. The cords of protoplasm 

 radiating from the nucleus are the persistent boundaries of the 

 vacuolar spaces of the " honeycombed " protoplasm. The nucleus 

 itself, according to Hanstein, is dragged out of shape, as it were, 



