38 Overton . — On the Organization of the Nuclei in the 
DISCUSSION. 
The Permanence of the Chromosomes. 
The majority of botanical as well as zoological writers recognize two 
essential parts of the nuclear reticulum. The linin, consisting of fine 
granules or thready substance, forms the general framework of the nucleus. 
My observations in general confirm these conceptions. I find a substance 
staining like portions of the cytoplasm present in the nucleus. This 
substance I have called the linin framework. It is in all probability a linin- 
like substance, although it seems to be quite distinct from the linin intervals, 
which connect the prochromosomes. 
Rosen (’92) describes two sorts of nucleoles, eunucleoles and pseudonu- 
cleoles, the latter of which are identical with the chromatin. Zacharias (’95) 
also distinguishes two kinds of nucleoles in Cticiwbita Pepo , one of which is 
chromatic in nature. 
Rosenberg (’04) in studying the resting nuclei of Capsella , Zostera , and 
Calendula came to the very important conclusion that the chromosomes are 
represented in the extreme resting condition of the nucleus as definite 
bodies, which are to be identified, as he noted, with the pseudonucleoles of 
Rosen and Zacharias. He comes to the conclusion, ‘dass die Chromosomen 
nicht etwa im Ruhestadium im Kern aufgelost werden, sondern noch weiter 
bis zuletzt, wenn in etwas modifizierter Form, ihre Selbstandigkeit beibe- 
halten und also einen immer vorhandenen Teil, ich mochte sagen, Organ des 
Kerns ausmachen. 5 There can be no question, as Rosenberg (’07) in his 
work on Hieracium notes, that the prochromosomes, which I (’05) have 
found and described both in somatic and pollen mother-cells and which he 
has found in the pollen mother-cells of Hieracium, may well be likened to 
these bodies. 
Laibach (’07) has repeated Rosenberg’s work on Capsella, and also 
found chromatic collections corresponding in number to the chromosomes 
in several other Crucifers, but believes that each such collection represents 
a centre, about which the greater part but not all of the material of the 
chromosomes is collected. Not all nuclei among the Cruciferae show these 
centres or the chromatic collections. 
Yamanouchi (’06) observed that in the nuclear reticulum of Polysi- 
phonia chains of chromatin granules appear in irregular rows, which he 
regards as the ‘ beginnings of the chromosomes’, and believes these structures 
are similar to the prochromosomes which I have described. These pro- 
chromosomes gradually become more pronounced and homogeneous to form 
the chromosomes as they appear in division stages. 
In his investigations on pollen mother«cells of certain Monocotyledons 
