No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 395 



concludes that the nucleolar substance, dissolved in the nuclear 

 sap, may be used in the production of the spindle fibers. 



Koernicke ('96), study of mitosis on Tritiaim : in the devel- 

 opment of the embryo sac when the two pole nuclei fuse 

 together, the two nucleoli also join to form one. In the mitosis 

 of the pollen the nucleolus always disappears before the forma- 

 tion of the spindle, but it could not be determined whether it 

 takes any part in the formation of the latter. 



Lauterborn ('96), nuclei of diatoms: there are several nucleoli 

 present ; in the spirem stage of division they commence to 

 gradually disappear ; " es scheint mir ziemlich sicher, dass ihre 

 Substanz mit derjenigen der Chromatinkornchen und des 

 Liningeriistes zur Bildung der Knauelfaden verbraucht wird." 

 It is important to note that the central spindle arises outside 

 of the nucleus, before the nucleoli begin to disappear, so that 

 there can be no genetic connection between the two. 



Poirault and Raciborski ('96), binucleated ("conjugate") 

 Uredineae during the production of the ascidiospore generation : 

 in the mitosis the nucleolus becomes extruded into the cyto- 

 plasm, almost always in the equatorial plane. " Bei manchen 

 Arten bleiben sie sehr lange erhalten so z. B. bei P.eridermiutn 

 Pini acicola, wo neben den langst ruhenden, mit neuen Nukleo- 

 len versehenen Kernen noch in den Plasma, die alten Kern- 

 korperchen der Elternkerneherumirren. Mit den Centrosomen 

 haben somit diese extranukleolaren, vakuolirten Nukleolen 

 nichts zu thun." 



Zimmermann ('96), a general critical summary upon the 

 vegetable nucleolus, with consideration of a part of the previous 

 literature. Nucleoli are almost always present in the cells of 

 the higher plants, and are of wide occurrence also in the lower 

 forms ; double staining serves to differentiate them from the 

 chromatin. There are usually from one to three to a nucleus, 

 but in the embryo sac of Lilinni martagnon there are from 

 twenty to thirty. In Cliara the older nuclei show the nucleolar 

 substance in the form of very numerous, irregular fragments. 

 The distinction of " Hauptnucleolus " and " Nebennucleolus " 

 is not tenable, since the latter may be possibly chromatin 

 globules. " Mit dem Chromatingerlist scheinen die Nukleolen 



