454 



SPERMATOPHYTES (SEED PLANTS) 



gether, but they do not form close clusters as the staminate 

 cones do. 



The scales of the ovulate cones are considered too complex to 

 be called sporophylls, for each scale consists of an ovuliferous 

 scale (ovule-bearing scale) and a bract, the two being partly united. 

 Some morphologists think that the ovuliferous scale itself repre- 

 sents two sporophylls fused together. The megasporangia or 



Fig. 403. — The ovulate structures of the Pine. A, branch bearing four 

 ovulate strobiU, B, ovulate strobilus, showing the arrangement of scales 

 (X about 2); C, a view of the inner or upper side of a scale, showing the two 

 sporangia (s). 



ovules, two in number, are borne on the upper side and at the 

 base of the ovuliferous scale {Fig. 4-03). The scales are spirally 

 arranged and closely crowded, but during pollination they spread 

 apart, and the pollen can slide in between them and reach the 

 ovules. After pollination the scales close together again, and the 

 cone is made water-tight by a secretion of resin. After pollina- 

 tion the cone also changes from the vertical to the nodding 

 position. 



The ovules consist of an integument and a nucellus, and deeply 

 buried within the nucellus the four megaspores occur. The 

 ovules are arranged one on each side of the median line of the 

 scale, with the micropyles pointing downward. The integument 



