﻿1903] NUCLEAR MEMBRANE 3 1 1 



chromosomes. In his works on Cobaea and Gladiolus (i8g8, 

 1900) the writer called attention to the breaking down of the 

 nuclear membrane. Beyond stating that the observations made 

 on these forms have been confirmed by a study of the material used 

 in the present investigation, it will be unnecessary to describe the 

 process farther. It might be well, however, to call attention to 

 the fact that it seems to be a general occurrence in the higher 

 plants that the nuclear membrane breaks down either immedi- 

 ately preceding or during the process of spindle formation, and 

 that therefore the mother nucleus is at this period devoid of a 

 membrane. 



The second stage in which the nucleus is devoid of a mem- 

 brane may be observed in the young daughter nuclei previous to 

 the accumulation of the karyolymph. It is this second stage 

 which affords us an opportunity of following the course of 

 events w^hich leads to the formation of a membrane around 

 each daughter nucleus. Fig. i illustrates a stage in the pollen 

 mother cell of Passiflora coemlea immediately after the chromo- 

 somes have reached the poles of the spindle. Here the chro- 

 mosomes are shown still attached to the connective fibers of the 



+ 



spindle, but otherwise lie freely in the cytoplasm. Their indi- 

 vidual identity may be easily observed. This stage is of 

 very short duration, however, for the chromosomes soon fuse 

 together, forming a single mass of chromatin. This fusion of the 

 chromosomes is shown in Jig. 2. This large irregularly shaped 

 mass of chromatin comes in contact with the cytoplasm at every 

 point of its outer surface. With the hope of detecting the very 

 first indication of the formation of the nuclear membrane, many 

 preparations showing this stage were carefully studied, but in no 

 case could any trace of a membrane be found during this period. 

 The nucleus at this time consists of nothing but a large single 

 irregularl}' shaped mass of chromatin. 



This stage, however, like the first, is of very short duration. 

 The chromatin undergoes a change which is accompanied by the 

 appearance of small but very distinct lacunae within the chro- 

 matin mass. Fig. j shows two of these lacunae centrally situ- 

 ated. This is the first indication of the accumulation of karyo- 



