i86 GYMNOSPERMS 



GINKGO 



Probably no other living tree can trace its ancestry so far back as 

 Ginkgo, for, as we have noted, it can be recognized in the Liassic. It 

 is doubtful whether it exists today in the wild state. Travelers claim 

 that they have seen it growing wild in the forests of western China, 

 where, they say, it reaches a height of more than 30 meters, with a 

 diameter of 1.3 meters. If extinct in the wild state, it must have be- 

 come so recently, perhaps in the last two or three thousand years, or 

 the date may have been much later, even in the last hundred years; 

 for the passenger pigeon is extinct, although people now living can 

 remember when it was so abundant that immense flocks cast 

 shadows like big clouds. Ginkgo was kept alive by priests in China 

 and Japan, who cultivated it in temple grounds. Now, in cultiva- 

 tion, it is world-wide and hardy even where the winter temperature 

 reaches 2o°F. below zero. 



It is a beautiful tree of various aspects, for it may be tall and 

 slender; or it may have a trunk a meter in diameter, soon breaking 

 into widely spreading branches, so that the breadth may exceed the 

 height. Whether it ever reaches the reported 30 meters in height 

 is doubtful. A botanist should identify the tree which is being 

 measured. 



THE LIFE-HISTORY 



The life-history, especially its spermatogenesis and embryogeny, 

 has been so thoroughly investigated that the principal features are 

 well known. 



The stem. — In most cultivated specimens the trunk is strongly 

 excurrent and the outline steeply pyramidal: but as the tree gets 

 old — 50 or 60 years — it is likely to broaden, so that the outline is 

 rounded at the top. If the top of a young tree is cut olT, the branches 

 spread widely; so that the trunk of a tree a meter in diameter may 

 not be more than twice that height before it breaks into large spread- 

 ing branches (figs. 199, 200). 



As in many Coniferophytes, there are two kinds of branches, the 

 long branch and the short spur. The first growth is always of the 

 first type; and as the branch, or the main axis, increases in length, 

 it grows for a year as a long branch before any spurs appear. The 



