GINKGO AND THE MICROSPORAN Sando MECHANISMS 
OF THE SEED PLANTS 
EDWARD C. JEFFREY AND R. E. TorREY 
(WITH PLATES VII-IX) 
The genus Ginkgo has long excited interest as the sole survivor 
of a group which was formerly numerously represented by species 
and widely distributed geographically. It is the purpose of the 
present article to show that its microsporangial structures have 
an important significance from the standpoint of the interpretation 
of microsporangia of seed plants in general. It will further be 
indicated in the present investigation that the affinities of the 
Ginkgoales are not with the Cycadales, as is ordinarily assumed, 
but with the abietineous subtribe of conifers, which one of us, in 
numerous articles devoted to the anatomical structure of living 
and fossil conifers, has attempted to show are the most primitive 
living representatives of the coniferous stock. Two important 
memoirs dealing with the genus under discussion have appeared 
in recent years. SEWARD and GOwAN' have given an interest- 
ing account of the living Ginkgo, together with statements in 
regard to its extinct predecessors and its botanical affinities. More 
recently SPRECHER? has published an admirable description of the 
anatomical structures of the various vegetative and reproductive 
organs in the genus. 
The microsporophylls of Ginkgo are paired structures opening 
by means of a stomium along their inner faces. The opening 
mechanism is a jacket of cells, generally nucleated, with fibrous 
thickenings extending from the cavity of the mature sporangium 
to the epidermis. These thickenings are a structural feature of the 
mechanical layer, and are quite absent in the epidermal layer itself. 
*Contribution from the laboratories of Plant Morphology of Harvard University. 
* SEwarp, A. C., and Gowan, J., The maiden hair tree (Ginkgo biloba L.). Ann. 
Botany 14: tIOQ-154. ie. 8-10, 1900. 
* SPRECHER, ANDREAS, Le Ginkgo biloba L. 8vo. pp. 208. figs. 205. Geneva. 
1907. 
281] [Botanical Gazette, vol. 62 
