m'clung: cytology and taxonomy. 209 



mosomes. I think that a reconciliation of the apparently con- 

 tradictory facts of cytoplasmic localization and chrohiosome 

 control is not at all impossible. 



There is but one time in the history of an organism when 

 the production and arrangement of these specific materials 

 occur ; there is but one time when the biparental chromosomes 

 function in common and not as separate entities. These peri- 

 ods are coincident, and I cannot escape the conviction that they 

 are related as eifect to cause. We find the spermatogonia and 

 oogonia reduced by repeated divisions to an almost acytoplas- 

 mic condition, and at that point discover the chromosomes pair- 

 ing off. During a long period of association, in certain grass- 

 hoppers extending through the winter months, these chromo- 

 somes remain together, and, at the end, present themselves to us 

 as members of an entirely different cell, with a large, clear 

 nucleus and ample cytosome. In the egg the contrast between 

 stages is even more remarkable, but here also the nucleus 

 grows with the cytoplasm. 



From these observations we must conclude that if the nu- 

 cleus governs metabolism, and many observations tell us this 

 is true, the unusual condition of the nucleus is the cause for 

 the unusual growth of the cytosome. The possibilities for the 

 new growth are established by the unified activities of the 

 chromosomes from the two parents, I would conclude. But 

 the cytoplasmic growth is only one aspect of the change that 

 has been taking place at this time. The chromosomes them- 

 selves have been active participants in a series of interactions 

 that leave them modified in structure and function in many 

 cases, the only exception being such as govern Mendelian 

 characters. Undoubtedly the nature and amount of this inter- 

 action vary between the same chromosomes in different genera- 

 tions, and herein is the cause of variation. Once the chromo- 

 somes are separated in maturation, however, their character 

 is determined and they do not again alter in the germ-cycle 

 until another synapsis. I believe these views are established 

 by common observation. The descendants of two parents 

 rarely develop body characters much alike, but now and then 

 real twins appear and they are strikingly alike. The reasons 

 for this are not far to seek, for the twins are the product of 

 the same two germ-cells, while ordinary children are from 

 different cells in each parent. 



From the plant kingdom we may gain still further evidence 



