1 9 1 2 ] p A CE—PA RNA SSI A 



319 



them 



Saxif, 



The mother cell in synapsis is shown in fig. 87. It will be seen 



if 



the archesporium. This is the commonest condition in Drosera. 

 But frequently a parietal cell is cut off which divides, as is shown in 

 fig. 88, giving a row of two parietal cells above the mother cell. 



more 



more 



more than one cell reached the mother cell stage. The 



me 



the mother cell are shown in figs. 90 and 91. In some instances the 

 megaspores are not in a row, as Rosenberg (19) has shown in his 

 text iig. 27, B, which is similar to fig. 25 in Parnassia. So far as 



much material 



megaspore develops in Drosera. Not 



that the development of the other spores is not common as it is 

 in Parnassia. 



In Drosera, even in the mother cell stage (fig. 87), air spaces 

 begin to develop in the chalazal region of the ovule. These 

 spaces are quite large by the time the embryo sac has reached the 

 two-nucleate stage (fig. 92), and in the mature ovule they are at 

 feast as strikingly developed as in Parnassia. The embryo sac 

 occupies only the upper third of the nucellus even at maturity, 

 quite in contrast to Parnassia and Saxifraga. The nucellus also 

 begins to show its peculiar enlargement of cells. The outer layer of 

 nucellar cells, except those directly over the embryo sac, increase 



asm 



> 



the latter lies next to the inner side of the cell. This enlargement 

 °f the nucellar cells, as well as the air spaces, reduces the specific 

 gravity of the seed. Diels (5) says : 



They are by their constitution capable of floating. Holzner states that 

 the seeds of D. rotundijolia at a temperature of about 20° are capable of floating 

 f or about a month. 



In fig. 93 the third division in the sac is shown and enough of the 

 nucellus to show the differentiation in it. In one nucleus the 10 

 chromosomes may be counted. 



