GINKGO ALES 



199 



fore winter stops their growth, the sporogenous tissue is well de- 

 veloped, and may reach the mother-cell stage. Reduction of chro- 

 mosomes takes place as soon as growth is resumed in the spring. 

 Eight and sixteen are the x and 2x numbers. 



The female strohilus. — ^The ovules are borne, often in great num- 

 bers, on spur shoots (fig. 214). This branch shows an unusually large 

 number of peduncles bearing two full-sized ovules. Usually one of 



Fig. 214. — Ginkgo hiluba: long shoot with spur shoots bearing ovules. Many of the 

 peduncles bear two fully developed ovules. 



the two ovules aborts early. As may be seen at the extreme left, the 

 long shoot, with its spurs, has come from an earlier spur. It will be 

 noted that the leaves are merely rounded, with none of the bilobed 

 character. 



The bilobed condition is probably due to a vigorous early growth 

 of the two earliest veins, the leaf traces, which would cause the lobing 

 by growing faster than the parenchyma of the leaf blade. The leaves 

 on the spurs are very immature during the early development of the 

 strobili. It may be that the diversion of food materials to the rapidly 

 developing strobili may cause the leaves to grow slowly and evenly 

 at this early period, during which the contour of the leaf is being 



