708 ' THE AMERICAN NATURALIST.. [Vor. 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- . 
