CONIFERALES (PINACEAE) 259 



The chromosome numbers among gymnosperms seem to be pre- 

 vailingly 12 and 24, and the Pinaceae, so far as observed, conform 

 to this, counts having been made in Pinus (38, 40, 46, 51), Larix 

 (59), Thuja (72), Taxodium (76), Araucaria (104), and Callitris 

 (159). In Sequoia sempervirens Lawson (92) obtained counts of 

 16 and 32 in the endosperm and first spindle of the embryo; and the 

 same observer (93), without definite counting, has reported 9 or 10 

 as the approximate haploid number in Cryptomeria, and 8 and 16 as 

 the numbers in S dado pity s (175); while in Widdringionia Saxton 

 (159) has definitely counted 6 and 12. 



3. The gametophytes 



THE FEMALE GAMETOPHYTE 



The development of the female gametophyte (endosperm) and of 

 the archegonia of Pinaceae has long been known in outline for a few 

 forms, through the early investigations of Hofmeister (10, 13) and 

 Strasburger (15, 18, 22, 25, 31). The later investigations have 

 filled in the outlines and have included a much wider range of forms. 

 In general, the sequence of events is approximately uniform in all 

 the Pinaceae observed, but differences in detail have been discovered 

 whose significance and range are at present uncertain. It should 

 be remembered that the megaspore begins to germinate early in the 

 history of the ovule, that when its membrane becomes the boundary 

 of the embryo sac there is still much of the nucellar tissue to be 

 developed, and that the membrane continues to grow along with the 

 growing endosperm. 



The division of the megaspore nucleus is followed by a series of 

 simultaneous nuclear divisions, until a large number of free nuclei 

 have been produced. Early in this series of divisions the embryo 

 sac, with its increasing capacity, begins to become vacuolate, and the 

 large central vacuole restricts the free nuclei to the layer of cytoplasm 

 lining the wall (fig. 284). In this parietal position free nuclear divi- 

 sion continues. The number of free nuclei produced before wall- 

 formation is probably very indefinite. The case of Taxus (52), 

 with its eight successive divisions resulting in 256 free nuclei, has been 

 applied with too much assurance to Pinaceae. It may be that this 

 number is a very common one among Pinaceae, but Miss Ferguson 



