676 



A TEXTBOOK OF THEORETICAL BOTANY 



The nucleus of the microspore first divides into two and a wall is laid 

 down between them dividing the body of the spore into a very small pro- 

 thallus cell and a large portion called the tube cell because it later develops 

 into the pollen tube. The prothallus cell is flattened against the cell wall 

 and rapidly disorganizes, being overlaid by a thickening of the intine. 



Shortly after this stage the spores are shed by the bursting of the wall of 

 the sporangium along its under side. This occurs in May. When the 

 sporangia are empty the cone rapidly withers and drops off". 



The Female Cone 



The female cones are developed laterally in the axils of scale leaves. They 

 are usually produced in clusters in place of shoots of unlimited growth and 



Fig. 676. — Pitius sylvestris. Terminal portions of branches with young female cones 

 in spring (left) and summer (right) of their first year. 



on different branches from the male cones. They begin to develop during 

 the winter and are ready for pollination in the following spring (Fig. 676). 



The young female cone is small and reddish in colour, and like the male 

 cone consists of a central axis bearing outgrowths which are arranged spirally, 

 those at the base being smaller and sterile. Each of these outgrowths is made 

 up of two structures, the smaller of which is spoken of as the bract scale, 

 which is directly connected to the central axis, and the larger, the ovuliferous 

 scale, which develops on the upper surface of the bract scale (Fig. 677). 

 The bract scale is leathery and the ovuliferous scale is woody. The latter 

 is wedge-shaped, with its broad end outwards, and it develops so as to conceal 



