The Gametophytes of Taxus Canadensis Marsh

Microspore formation takes place in the autumn. There are no indications of prothallial cells. The pollen grain is uninucleate when shed. The pollen tube penetrates the nucellus very rapidly and enlarges excessively about the female gametophyte. Three divisions take place in the development of the male gametophyte. The body cell divides into two unequal male cells, the larger of which functions in fertilization. Several megaspore mother cells are formed, of which only one usually functions, although two of them may form megaspores. The megaspore mother cell is the usual winter condition, but megaspores may be formed and the female gametophyte may consist of several free nuclei before winter. Following the free nuclear stage of the female gametophyte, radical walls come in, closing the cavity before the appearance of periclinal walls. The archegonia appear early in the endosperm. The central cell is the functional egg, no ventral canal cell or ventral nucleus being formed. More than one female gametophyte in an ovule is common; as many as 5 were observed. In fertilization the nuclear contents of the pollen tube are discharged into the egg. A cytoplasmic sheath is formed about the two fusing nuclei. From pollination to fertilization may be as short as one month. Mature seeds have been collected 6 weeks later. In general the gametophyte history agrees with that reported for T. baccata.