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MORPHOLOGY OF GYMNOSPERMS 



neck of the archegonium, many of its cells being crushed. In the axis 

 of the advancing cylinder two growing points are soon established, 

 that of the stem at the end of the axis, and that of the root very close 



Fig. 247. — Ginkgo biloba: late stage of proembryo; the stem and root will be 

 organized from the small-celled tissue at the apex; X160. — After Lyon (39). 



to it, the two being separated by very few cells. Later the primordia 

 of the two cotyledons appear in the peripheral region of the cylinder, 

 beginning as crescentic mounds of tissue. From an examination of 

 mature seeds, Lyon (39) claims that the proembryo sometimes 

 gives rise to two embryos. 



