326 GYMNOSPERMS 



rounded by the spongy tissue, which is gradually absorbed. In later 

 stages, while there is not such a definite surrounding tissue as the 

 "endosperm jacket" of the cycads, the cells in contact with the 

 megaspore membrane are more or less modified, and some have 

 applied the term "tapetum" to these surrounding cells. 



The archegonia. — It would seem that most, or even all, of the su- 

 perficial cells at the top of the female gametophyte are, potentially, 

 archegonium initials. The number which becomes recognizable as 

 initials is small, and the number reaching maturity may be still 

 smaller. 



There are two general types of archegonial groups in conifers. In 

 the Abietaceae and many others, the archegonia are separated by 

 vegetative cells of the gametophyte. In the Cupressaceae and 

 Taxodiaceae they are in contact with each other, forming an arche- 

 gonium complex. In some, the complex is at the apex of the gameto- 

 phyte, as in Thuja, Libocedrus, Tetraclinis, and Juniperns; while in 

 others it is lateral, as in Sequoia, Actinostrobus, Callitris, and Wid- 

 dringtonia. 



The number of archegonia is much larger where there is an arche- 

 gonium complex than where the archegonia are separated by vegeta- 

 tive tissue. In Thuja the number is usually 6; in Juniperus com- 

 munis, 4-10, usually 7; in Libocedrus decurrens, 10-15; in Biota 

 orientalis, 9-24; in Callitris verrucosa, 17-20; in Actinostrobus pyr- 

 amidalis, 25-30; in Widdringtonia cupressoides, 30-100, variously 

 placed, but never apical; and in W.juniperoides the number reaches 

 200. 



In forms with archegonia separated by vegetative cells, the num- 

 bers are smaller and the position nearly, but not quite, apical; for 

 the archegonia are usually in a circle, surrounding the center. In 

 Pinus strobus, P. rigida, and P. resinosa, the usual number of arche- 

 gonium initials is 3; in P. laricio, there are usually 5, occasionally 6, 

 and sometimes only 2 or 3. In Torreya taxijolia,^^^ there is almost 

 invariably only i archegonium; but in other genera a single arche- 

 gonium is very rare. Both types, the separated archegonia and the 

 archegonium complex, occur in Sequoia. 



The archegonium initial first becomes recognizable by elongating 

 and enlarging somewhat, while the adjoining cells divide. Its nu- 



