CONIFERALES (TAXACEAE) 329 



growth in Taxus (icxi). When the mother cells are more than 

 one, several of them may begin to function. This functioning 

 of more than one mother cell may not reach the synapsis stage, as 

 observed in Taxus (100), or it may proceed until the gametophytes 

 are well formed, as has been reported in one case of Podocarpus 

 coriacea (cultivated in Jamaica), in which two gametophytes were 

 observed in one ovule (69), and in one of them there were tracheids. 

 If the presence of tracheids in female gametophytes means sporophytic 

 tissue, as has been shown among ferns, this is a case of incipient 

 apogamy. 



The number of chromosomes in Taxaceae has been determined 

 for very few forms. In Podocarpus (139) the numbers are 12 and 24, 

 conforming to the numbers among the Pinaceae, so far as observed; 

 but among the taxads they have been found to be 8 and 16 in Taxus 

 (100) and Torreya (99). Whether this is a feature of the taxads, 

 in contrast with the podocarps and Pinaceae, is a question that remains 

 to be answered. 



3. The gametophytes 



THE FEMALE GAMETOPHYTE 



The development of the female gametophyte follows the general 

 course described for the Pinaceae (p. 259), with free nuclear division, 

 parietal wall-formation, and centripetal growth until the embryo sac 

 is full of tissue (fig. 381). The vacuolation of the sac depends upon 

 the rate of its growth; but in general it occurs so that the free nuclei 

 become parietally placed from the 2-nucleate to the 32-nucleate stage. 

 Actual counts of the number of free nuclei before wall-formation have 

 been made for Taxus (52) and Torreya (loi), and found to be 256, 

 representing eight successive divisions. Probably this represents the 

 usual number of free nuclear divisions among conifers, although it 

 must be expected that great variation and irregularity may occur. 

 The behavior of the nuclei in the endosperm-formation of Taxus 

 has been studied in detail by Strasburger (100), and no fusions or 

 unusual conditions were discovered, as have been described for some 

 of the Pinaceae. An idea of the amount of endosperm growth may 

 be obtained from measurements made in Torreya taxifolia (loi). 

 At fertilization the endosperm consists of 400-800 cells and measures 

 20 by 30 At; while in the mature seed it measures 14 by 20 mm. 



