THE PHASE OF THE NUCLEUS KNOWN AS SYNAPSIS. 601 



none of these growing stages is the nuclear cavity spherical in form. It is invariably 

 oval or egg-shaped. As soon, however, as the mother-cells are practically free from 

 one another, as illustrated in figs. 26 and 27, the nuclear cavity assumes an almost 

 spherical form. Here the internal pressure is apparently exerting itself equally in all 

 directions. These facts not only show that a great internal pressure exists within the 

 nuclear cavity, but also that the effect of such a pressure on the resultant growth and 

 form of the nuclear cavity is controlled by surrounding resistance. This being the 

 case, the internal pressure would naturally exert itself in the line of least resistance, 

 and that would be towards the intercellular space. The conditions shown in figs. 20, 

 21, 22, and 23, would seem to indicate that this is exactly what has taken place. In 

 this I see a reasonable explanation for the lateral position of the chromatin mass during 

 the growth period. It is simply the result of the enlarging nuclear cavity extending 

 out towards the intercellular space where there is least pressure from the neighbouring 

 cells and leaving the chromatin mass behind in its original position. Considering all of 

 the circumstances under which the mother-cells are developing, the lateral position of 

 the chromatin mass during the growth period is a perfectly natural one. 



The object of the present paper is simply to state my interpretation of that phase of 

 the nuclear cycle commonly known as synapsis and also the reasons for such inter- 

 pretation. I do not intend in this work to go into the details of reduction — this will be 

 published shortly in a separate paper. I may state, however, that I have strong 

 evidence for believing that the reduction process cannot take place in Smilacina during 

 the growth period. In figs. 26 and 27 we have represented stages in the development 

 of the mother-cells which are undoubtedly much later than that known as synapsis. 

 Here we have a condition where the chromosomes may be observed with sufficient 

 clearness that they may be counted. After repeated counting I estimated that the 

 number at this time is twenty, which is just twice the number found in the haploid 

 phase. The real act of reduction is shown in fig. 28, which is at a time much later than 

 that shown in fig. 27. 



Summary. 



Spore-mother-cells, being both storage and merismatic in their function, present an 

 organisation that is strikingly different from that found in ordinary vegetative tissue. 



Being charged with food substances for the production and sustenance of four 

 spores, they are devoid of vacuoles of any measurable size in the cytoplasm. 



During their development, however, there is a great accumulation of sap within the 

 nuclear cavity, which causes a great osmotic pressure in the same manner that the cell- 

 sap does in the vacuole of growing vegetative cells. 



The pressure, acting from within, causes the nuclear membrane to distend and the 

 nuclear cavity to expand. 



This expansion, at first gradual, continues until the nuclear cavity grows to twice 

 or even three times its original size. 



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