The individuality of the chromosomes and their serial arrangement, etc. 129 



beadlike bodies, and the serial arrangement can be traced in part. These 

 chromatin bodies are certainly not more numerous than the haploid 

 number of chromosomes. 



Meanwhile the three microspore nuclei which were crowded into the 

 apex of the old mother-cell have disintegrated. Juel considers that in 

 Carex acuta these three nuclei after forming spindles for division fail 

 to complete the mitosis and return to a resting stage. I have not been 

 concerned especially with this point, but my preparations indicate that 

 there is more or less irregularity in the division of these three nuclei, 

 and that as a result from three to six nuclei may be found at the apex. 

 Juel, as I judge, shows five nuclei in this position in one of his drawings 

 (Juel 1900, fig. 42). At first plasma membranes mark the boundaries of 

 these cells (fig. 33). Later they become shriveled into compact masses 

 which are closely pressed into the apex of the mother-cell wall. The 

 central cytoplasmic mass is separated from these degenerating nuclei 

 by a plasma membrane. 



The mature pollen grain consists of a large vegetative cell in the 

 cytoplasm of which are two germ cells each with a clearly defined plasma 

 membrane. The wall of the old spore mother cell evidently becomes a 

 part of the wall of the mature pollen grain. 



Discussion. 



It is evident from the above account that in Carex aquatilis the 

 chromosomes can be observed as unit masses at all stages of nuclear 

 development, except during synapsis and the thick spirem stage which 

 follows it. The arrangement of these units in series is also a conspicuous 

 and rather uniform feature. 



The earlier evidence supporting the doctrine of the individuality 

 of the chromosomes has been quite fully summarized by Boveri (1904). 

 The evidence is based largely (1) on the uniformity in the number and 

 character of the chromosomes appearing in successive divisions, (2) on 

 the proof that whenever more or less than the usual number of chromo- 

 somes enter a nucleus in the eggs of Ascaris the same number always 

 appears in later divisions of that nucleus, (3) on the evidence that the 

 loss of chromosome identity during the reticulated condition is only 

 apparent, (4) on the proof that nuclear fusion doubles the number of 

 chromosomes while the reduction division decreases the number by 

 half. Boveri extended the conception of individuality to the extent of 

 regarding the chromosomes as elementary organisms rather than merely 

 permanent cell organs. 



Archiv f. Zellforschung. IX. 9 



