Fertilization in Pinus Strobns . 
453 
observed in the division of the * segmentation nucleus/ but 
was not sketched because of lack of space. A similar stage 
in the division of one of the four nuclei of the proembryo is 
shown in Fig. 80 b. 
In general the chromosomes at the nuclear plate are in the 
form of U’s and V’s; in rare instances they are long and 
somewhat coiled, and the spindle-fibres are not attached to 
their centres (Figs. 61-64). They pass to the poles as narrow 
U’s (Fig. 66). Sometimes the arms of the U are pressed so 
closely together that the chromosomes look like longitudinally 
split rods. In a late anaphase of the division, the chromatic 
elements present a crinkled appearance, and the poles of the 
spindle terminate in granular areas from which threads extend 
into the surrounding cytoplasm. These fibres may be quite 
inconspicuous or they may be very prominent, frequently 
forming fantastic figures (Figs. 67 and 68). 
A portion of the achromatic constituents of the sexual 
nuclei may persist in the region of the mitotic figure until the 
formation of the daughter-nuclei, but, as a rule, all traces of 
the original nuclei have disappeared at this time. Blackman 
finds no suggestion of a cell-wall in connexion with the first 
division which takes place within the oosphere. But here 5 
again, great variation has been found in Pinns Strobus . The 
spindle either becomes constricted at the centre with little or 
no sign of thickening along its median line, or it may be very 
broad, in which case prominent thickenings occur, only to 
disappear at a later stage, in the line of the cell-plate (Figs. 
66 and 69). As the half-chromosomes unite to form the 
daughter-nuclei, the poles of the spindle often become very 
slender, and seem to press against the forming nuclei, render- 
ing them concave along their inner surfaces ; and delicate 
fibres now extend from all sides of the division-figure into 
the cytoplasm (Fig. 69). As already indicated, there is no 
evidence that any portion of this spindle is derived from the 
cytoplasm, and it is probable that a large part, if not all, of 
its fibres are formed by a rearrangement of a portion of the 
achromatic, nuclear reticula. During the dissolution of the 
H h % 
