CHAPTER XIV 

 CONIFEROPHYTES— CONIFERALES— CowZ/m^gf^ 



THE FEMALE GAMETOPHYTE 



The megaspore is the first cell of the female gametophyte. The 

 megaspore mother-cell, in the two divisions by which the four mega- 

 spores are produced and the number of chromo- 

 somes is reduced from the sporophyte number 

 {2x) to the gametophyte (x) number, is usually 

 so deeply placed in the nucellus, when it first be- 

 comes recognizable, that its origin looks indef- 

 inite. In all cases in which the origin can be rec- 

 ognized with certainty, the archesporial cell is 

 hypodermal, and its first periclinal division gives 

 rise to a tapetal cell and the megaspore mother- 

 cell. An axial row of four megaspores has been 

 observed in many cases (fig. 319). 



It happens, frequently, that there is a row of 

 only three cells. In such cases, the upper cell, re- 

 sulting from the first division of the megaspore 

 mother-cell, fails to divide, and does not reach 

 the megaspore stage. The lower cell divides and 

 produces two megaspores, the lower one of which 

 continues to develop, while the other, together 

 with the upper cell of the row of three, disor- 

 ganizes. The failure of a division in the upper 

 of the first two cells was noted in the cycads, 

 Stangeria^^ and Ceratozamiaf^^ but Zamia,^^^ the 

 most advanced of all cycads, has a row of four. Since, in nearly all 

 cases, only one megaspore germinates, it is natural that there should 

 be a tendency to ehminate the useless spores. 



The first indication of germination is an enlargement of the mega- 

 spore and its nucleus. After the first division of the megaspore 



321 



Fig. 319. — Finns 

 laricio: row of four 

 megaspores, the lower 

 one growing vigorous- 

 ly and the other three 

 aborting; X8io. — 

 After Dr. Margaret 

 Ferguson."'^ 



