171 Plant Cytology. 193 



This, I think, is a mistaken view. Both exhibit an equal 

 degree of plasticity. 



With the evidence now before us, I would suggest that 

 every cell consists of tlie general protoplasm and of the nucleo- 

 plasm, these together constituting the vegetative substance of 

 the cell, while the linin and chromatin or chromosome sub- 

 stance constitute the hereditaiy substance of the cell. In many 

 cells the latter is chiefly aggregated in the nucleolus during 

 the resting phase. From the nucleolus threads radiate out 

 through the nuclear area and fuse to form the nuclear mem- 

 brane, while from it radiating prolongations traverse the proto- 

 plasm. Whether such threads are continuous from cell to 

 cell through pores in the common walls is a question still 

 needing solution. 



The Endonucleohis. — At a time when the nucleolus was 

 regarded as of small moment, I noticed as a uniform feature 

 within it, in embryonic cells, a small clear body which was 

 named the endonucleolus. Its constant presence in a wide 

 range of tissues warranted me in regarding it as an element 

 of possible importance in cell life. In recent years it has 

 generally been spoken of as the nucleolar vacuole, and has 

 been viewed as an inconstant factor. Meunier's statement that 

 it is absent in living cells of Spirogyra is unquestionably 

 erroneous, though owing to the great density of the nucleolus 

 it is frequently difficult of detection. If we are content to 

 call it a vacuole, this will depend on the meaning which may 

 attach to the term. That it is often overlooked in embryonic 

 tissues is to be explained by the overstained state of prepara- 

 tions. I would still insist on its general occurrence and 

 probable importance in living cells. Montgomery (p. 508) 

 says : "In opposition to Meunier, and in agreement with most: 

 investigators, I must conclude that vacuoles are normal struc- 

 tures in nucleoli, since they may be seen after the most 

 diverse methods of fixation, and their size and number are 



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