No. 449.] STUDIES ON THE PLANT CELL. 



373 



erally transitory as in Corallina, Davis '98, where the structure 

 (Fig. I c) is only found in the young daughter nucleus and later 

 fragments into many smaller bodies. In Spirogyra however 

 (Moll '94, Mitzkewitsch '98, Van Wisselingh :oo, '02) the 

 chromatin is supposed to be always in a globular mass mixed with 

 nucleolar substance and recalls the conditions in certain Protozoa. 

 These chromatic structures however should never be confused 

 with nucleoli, whose substance is different and which are not 

 permanent in the cell, since they may disappear before or during 

 nuclear division and be formed dc novo in each daughter nucleus. 



The substance of the nucleolus is not well undcrstKod it is 

 frequently impossible to distinguish it from clironiatin L\cc])t 

 when favorably situated in the cell and there is nuk h in idciu e 

 that it is closely related to that substance. In lar-c inu Ici of 

 higher plants the chromatin is sometimes <;athcral into -lobular 

 bodies without apparent relation to a linin thread and these are 

 readily mistaken for nucleoli and have been called such, but this 

 loose usage of the term should be avoided. And true nucleoli 

 may be so closely associated with the linin net work as to have 

 the appearance of chromatin. Some of these conditions have 

 been especially described by Cavara, '98. Chamberlain. '99. has 

 made a study of the egg nucleus of the Pine where mas^es of 

 chromatin may take very irregular forms on the linin threads 

 (Fig. I e) and sometimes resemble small nucleoli. Hut such 

 conditions should always be sharply distinguished Irom true 

 nucleoli which are often caught in the meshes of the linin net 

 work and appear to be a part of it when in realit\- there are no 

 organic attachments. It is certain that nucleoli are of secondary 

 importance in the cell and probably by-i)roducts of the general 

 constructive activities of the nucleus. In which ca.se they may 

 be secretions, perhaps closely related to chromatin, or even direct 

 transf(,rmati(ms of this substance. It is well known that the 

 nucleus has wonderful constructive powers, when the amount of 

 chromatin and other nuclear substances may be nnmensely 

 increased, facts that are especially well illustrated at reproductne 

 periods of the plant's life as during siM.rogenesis and gameto- 

 genesis. 



Chromatin is the only substance in the nucleus that is constant 



