GINKGOALES 



205 



larger cell divides again, producing another prothallial cell, and a 

 larger cell which is the antheridial initial. The first prothallial cell 

 soon aborts, but the second is persistent. The antheridial initial di- 

 vides, producing a generative cell, in contact with the second pro- 



FiG. 221. — Ginkgo biloba: axis with 

 seven ovules, each borne singly on a 

 peduncle, not in pairs. Each peduncle 

 has two bundles instead of the four 

 which appear when the peduncle bears 

 two ovules. — After Sprecher.s'^ 



Fig. 222. — Ginkgo biloba: early 

 development of the male gameto- 

 phyte; A, first prothallial cell and 

 inner cell; B, second prothallial cell 

 and inner cell dividing to form the 

 generative cell and tube cell; C, mi- 

 tosis in antheridium initial; D, first 

 prothallial cell (aborting), second 

 prothalHal cell, generative cell, and 

 tube cell — the shedding stage. The 

 exine is shaded with lines. It does 

 not cover the top of the pollen grain. 

 The intine is represented only by a 

 line. It alone covers the top of the 

 pollen grain; X770. — From Cham- 

 berlain, Methods in Plant Histol- 

 ogy"y (University of Chicago Press) . 



thallial cell, and an inner cell, the tube cell, which does not divide 

 again. In this four-celled condition the pollen is shed (fig. 222). If fe- 

 male trees are within 200 meters, some pollen will reach the polHna- 

 tion drops and there will be some seed. If there are female trees 

 within 100 meters, pollination is likely to be so abundant that most 

 of the ovules will be pollinated. 



The exine does not cover the entire pollen grain, being lacking at 

 the top, which is covered only by the intine. Upon reaching the 



