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SEXUAL DIMORPHISM AND VARIATION IN GINKGO 



BILOBA, L. 



By X. M. Grier 



Nurserymen claim to be able to distinguish the sex of this tree 

 by the habit assumed. According to their observations, the 

 male tree while retaining the conical type of stem characteristic 

 of the family, tends to approximate the columnar aspect as ex^ 

 hibited for instance in the Lombardy poplar. On the other 

 hand they state the outline of the female tree is far broader at the 

 region of lowest branching, i. e., the outline of the female tree is 

 a cone with a much larger base than that of the male. Personal 

 observation of the fruiting trees seemed to confirm the difference 

 claimed by the nurserymen, although some intergrades were 

 found. The available literature contained no reference to any 

 sexual dimorphism whatsoever nor to the following distinction 

 between male and female trees based on leaves taken from the 

 lower branches of 5 trees in the Shaw Botanical Garden and 

 Tower Grove Park in St. Louis. 



As has probably been observed, 'a large proportion of leaves of 

 ginkgo are entire or devoid of true lobing, although they may 

 become frayed and indicate a false division. Of a total of 535 

 leaves examined from 2 male trees, 322 showed a true lobing, 

 generally into 2 well marked, but often 3 or 4 divisions less marked 

 — 60 per cent. In the 3 female trees, the proportion of bilobed 

 or divided leaves is much less, 103 of 645 or 13 per cent, of the 

 total. This condition of greater abundance of dissected leaves 

 in the male seem to correlate with the distinction made by the 

 nurserymen. The female tree, a broad-based cone consisting of 

 excurrent trunk with branches diverging therefrom from base to 

 apex at a constantly decreasing angle, would not require the 

 same adaptation for lighting that the spire-like contour of the 

 male would, which therefore may account for the greater abun- 

 dance of dissected leaves in the male. 



Central High School, 

 St. Louis, Mo. 



