i37 
Spore Formation in Torreya californica. 
■division and the longer narrower chromosomes of the succeeding 
homotype was quite clear in some cases (cf. Figs. 10c and lOd). 
The two daughter-nuclei which result from the first division are 
sometimes of great breadth (Fig. 10b). The second division 
may occur before or after the formation of a wall between the first 
two daughter-nuclei (cf. Figs. 10a and lOd). The second division 
commonly takes place in such a way as to give rise to a tetrad, but 
sometimes the four microspores lie in one plane (cf. Figs. lOg and lOd). 
Starch is abundantly present in the cells during these divisions. 
At a slightly later stage the tetrads are found to have separated 
completely from one another, while only a trace here and there 
remains of the walls of the mother-cells. Some of the pollen- 
grains are grouped in pairs, suggesting that they have been produced 
by a single division of the mother-cell. The nuclei of the tapetal 
layer are poorly provided with chromatin, and some of the cells are 
bi-nucleate (Fig. 11). On April 28th nearly all the pollen-grains 
have dropped apart; they are uni-nucleate and contain a certain 
amount of starch, though less than was the case three weeks before. 
It seems probable that the starch was to some extent used up in 
forming the walls of the pollen-grains, which are thicker than those 
of the mother-cell, though they have not yet attained to their 
ultimate thickness. Ten days later the quantity of starch has so 
much increased as to obscure the nucleus in hand sections. 
IV. —The Germination of the Microspores. 
By May 31st in material collected in 1902 (Fig. 4c), the pollen- 
grains have become bi-nucleate, but in 1904 this stage was reached 
a fortnight sooner. In dividing into two cells whilst still enclosed 
in the pollen-sac the pollen-grains of Torreya agree with those of 
Cephalotaxus and differ from those of Taxus 1 . Different stages of 
the division of the microspore can be found in the same cone—the 
resting nucleus, the spirern, the spindle, and the two daughter 
nuclei still united by threads (Figs. 12a—d). At first the two 
daughter nuclei lie near together in the middle of the cell, and both 
have a similar granular appearance and contain nucleoli. But one 
/presumably the generative nucleus) soon retires to one side of the 
grain, and becomes oval, homogeneous, and Safranin staining, while 
the other retains its central position and shows no change of 
structure (Fig. 12e). Coker’s figure of the corresponding stage in 
1 E. Strasburger. Ueber das Verhalten des Pollens und die 
Befruchtungs-Vorgange bei den Gymnospermen, Jena, 1892. 
