RECENT ADVANCES IN VEGETABLE CYTOLOGY. 31 



growth, maturity and senescence of the cells. Some ex- 

 tremely interesting results in this direction have recently been 

 published by Zacharias (8). An ordinary resting nucleus 

 consists, as all biologists are aware, of a somewhat dense 

 thread-like framework, often spoken of as linin, which 

 usually exhibits copious anastomosis, sometimes to such a 

 degree that it almost forms a spongy texture. In this 

 framework granules are found embedded which react 

 definitely to stains and to solvents ; they constitute the 

 nuclein, a phosphorus-containing substance which at the 

 periods of nuclear division undergoes an enormous increase 

 in bulk. The linin is bathed in a more fluid substance, the 

 paralinin. One or more spherical bodies, the nucleoli, 

 are often present in addition to the foregoing constituents, 

 and the nucleus is delimitated from the cytoplasm by a 

 pellicle or membrane. The nucleolus contains, as was 

 shown by Zacharias many years ago, at least two 

 substances, one of which is of an albuminous nature, and is 

 dissolved out on treatment with gastric juice ; after peptic 

 digestion has extracted the albumin, a substance is left 

 which Zacharias calls Plastin. Now observation shows 

 that the relative proportion of these two constituents varies 

 considerably at different periods of the life of the cell, and 

 this is of importance in connection with the intricate series 

 of changes which the nucleus passes through during the 

 process of ordinary division. The conviction has slowly 

 been forced upon us within the last few years that there 

 exists a considerable variety amongst the bodies which 

 have been included in the common term of nucleoli. 

 Auerbach (9) showed in 1890 that some of them 

 absorbed certain red dyes with greater avidity than they did 

 certain blue ones, whilst other nucleoli reacted in the oppo- 

 site manner. He thus distinguished between erythrophil 

 and cyanophil nucleoli. These results have been extended 

 to plants by the investigations of Rosen (10) and others, 

 but especially by Zacharias, who has applied the test of 

 solvents to them, with the result that the difference between 

 the two classes of nucleoli proves to be a much more real 

 one than had hitherto been supposed. And these observa- 



