(500 MR A. ANSTRUTHER LAWSON ON 



cavity very much enlarged, but not perhaps to the extent of these mother-cells. These 

 latter cells have an important and varied series of functions to perform, and their 

 organisation is modified accordingly. Not the least of these modifications I believe to 

 be the taking on of the function of the vacuole by the nuclear cavity. While this 

 cannot be actually proved, I think the evidence is sufficient to warrant my offering it 

 as an explanation for the occurrence of the "growth period" of the nucleus at this 

 particular phase in the life-history — a phase that is commonly known as synapsis. 



The majority of writers on the subject have made much of the lateral position of 

 the chromatin mass within the nuclear cavity during the " synaptic period." The mass 

 is invariably described as occupying a position at one side of the cavity, close to the 

 nuclear membrane. This position, I think, is responsible in a large measure for the 

 contraction idea, for it certainly gives one the impression of a shrinkage or withdrawal 

 from the membrane. More than one writer has described the chromatin as havino- moved 

 bodily from one side of the cavity to the other— Cardiff (1905) even goes so far as to 

 state that this lateral position is due to gravity. If there had been a ' ' violent contrac- 

 tion," as one writer describes it, the lateral position would seem obvious enough. If, 

 however, there is no contraction whatever, there must be some reason for this peculiar 

 and characteristic condition. 



I have above called attention to the fact that the young spore-mother-cells, compos- 

 ing the Archesporium, lie closely together, forming a dense mass of tissue with very 

 thin walls and no trace of intercellular spaces. The straight lines and sharp angles 

 that mark the boundaries of the cells are shown in figs. 1, 2, 3, 4, and 5. As these 

 cells grow in size, there is also a growth taking place in the anther as a whole, and, 

 as development advances, there is more room within the sporangium for the mother- 

 cells to enlarge. Now, these cells not only enlarge but, as everyone knows, they later 

 separate from one another and eventually lie free in the mother liquor of the anther. 

 This separation of the mother-cells from one another first manifests itself by the presence 

 of small intercellular spaces. After an examination of many sections I find these spaces 

 occur more frequently at the angles where two or more cells meet. At such poinds the 

 thin cell-wall becomes rounded off (figs. 15, 17, and 18), clearly indicating that the 

 internal pressure was exerting itself towards the intercellular space. This rounding off 

 of the angles of the cell-wall proceeds exactly with the development of the intercellular 

 spaces, until we finally have the rounded or oval shapes of the cells as shown in the figs. 

 20, 21, 22, 23, 24, etc. It is quite clear from these figures that the growth of the 

 '•ells has taken place in a direction towards the first intercellular space that is formed. 

 Nearly all of the cells become more or less oval in outline, but one end is always more 

 rounded than the other. The latter end invariably shows the wall in straight lines and 

 angles, indicating contact and pressure against its neighbours (figs. 22, 23, and 24). 

 The rounded end is always free and exposed to the intercellular space. Now, if we 

 examine any of these stages that are figured, we will find that the enlarged nuclear cavity 

 is always extended towards the rounded end of the cell. It will also be found that in 



