708 THE AMERICAN NATURALIST. [VOL. XXXIX. 



substance does not seem to contribute directly to the chromo- 

 somes and these have been regarded as secretions within the 

 nucleus. Strasburger believed that such were masses of reserve 

 material drawn upon by the kinoplasm during the process of 

 spindle formation. The term plastin has been applied to such 

 substance in the nucleolus and also in the linin as cannot be 

 directly connected with chromatin. A nucleolus may consist of 

 plastin alone, or have with this substance varying quantities of 

 chromatin. Nucleoli consisting of chromatin alone may be ex- 

 pected among the lower plants from the studies on Spirogyra, 

 Corallina, Sphaeroplea, and Nemalion. Plastin and chromatin 

 are probably closely related substances. 



A recent paper of Wager (: 04) indicates that the nucleolus 

 of some higher plants holds a far closer relation to the chromo- 

 somes than has been supposed and rather weakens Strasburger' s 

 theory of the structure as a reserve mass drawn upon during 

 mitotic activities. This study and recent papers by Miss Mer- 

 riman (: 04) and Mano (: 04) have all been upon the cells of root 

 tips while the conceptions of Strasburger and others have been 

 founded largely on the structure and behavior of the nucleolus 

 in the spore mother-cell during the mitoses of sporogenesis. 

 Wager treats of the root tip of Phaseolus, Miss Merriman of 

 Allium, and Mano of Solanum and Phaseolus. They are impor- 

 tant contributions to the subject of the nucleolus and should be 

 considered in any treatment of this structure. The papers 

 appeared too recently to be noted in our brief account of 

 the nucleolus in Section I which is consequently incomplete. 

 Wager's paper especially presents an excellent review of the 

 literature on the nucleolus in the plant cell. 



Wager concludes that the nucleolus is really a portion of the 

 nuclear network and that the spirem is derived in part at least 

 from this structure. Material from the nucleolus then passes 

 into the chromosomes. Also, in the reconstruction of the 

 daughter nuclei the chromosomes are massed together at a cer- 

 tain stage and from this mass the nucleolus emerges, taking out 

 with it the greater part of the chromatin. Wager then con- 

 siders the nucleolus as a store of chromatin which must be 

 taken into account in theories of heredity based on the morpho- 



