SPERMATOPHYTA 



347 



(3) centripetal growth until the gametophyte is cellular throughout. A 

 deeper region of nutritive tissue is usually differentiated fromamicropylar 

 region of smaller cells in which the archegonia develop. The number of 

 archegonia is highly variable. In the Abietaceae it is usually 2 to 5, but 

 in the other families the number may be much higher, reaching 200 in 

 extreme cases. 



A B 



Fig. 297. Ovule and archegonium of Pinus lambertiana. A, longitudinal section of 

 ovule, showing female gametophyte with two archegonia, XIO; B, mature archegonium 

 with two neck cells, a small ventral canal cell, and a large egg with a conspicuous nucleus 

 and many small food bodies, X85; m, micropyle; i, integument; n, nucellus; p, pollen tube; 

 a, archegonium; g, female gametophyte. 



Archegonial development follows the same pattern as in the Cycadales. 

 Sometimes only two neck cells are formed but generally there are many 

 more, the number varying from 4 cells in one tier to about 12 or more in 

 several tiers. In the Abietaceae a definite ventral canal cell is formed 

 that soon disorganizes (Fig. 2975). In the other families there is only a 

 ventral canal nucleus. In Torreya it is doubtful whether even this 

 is present, the nucleus of the central cell apparently functioning directly 

 as the egg nucleus. A special feature of the Taxodiaceae and Cupres- 

 saceae is the formation of an ''archegonium complex," an organization 

 of several archegonia in contact with one another and enclosed within 

 a common jacket. 



