352 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



obtains at present. Thus there are two species of Zamia in the 

 lower Eocene along the shores of the Mississippi embayment. A 

 third species occurs in the basal Eocene of Belgium, and a fourth in 

 the late Oligocene or early Miocene of Chile. Oligocene species include 

 a Zamia from France, an Encephalartos from Greece, and a not cer- 

 tainly identified Ceratozamia from northern Italy. The Miocene rec- 

 ords include a Zamites and a Cycadites from Switzerland. 



PHYLUM COXIFEROPHTTA. 



The Coniferophyta correspond almost exactly to the Gymno- 

 spermae of the older students. Their outstanding characteristic is 

 the exposed ovules discovered by Robert Brown in 1827. This fea- 

 ture has ceased to be diagnostic, since it is common to the Pteii- 

 dospermophyta and Cycadophyta, and is evidently of ancient line- 

 age. Although probably more continuously and abundantly repre- 

 sented in the geological record than any other group of plants, it 

 can not be said that our knowledge of either the comparative mor- 

 phology or the geological history of the phylum warrants a dog- 

 matic view of their phylogeny. 



All the known coniferophytes are woody plants with pronounced 

 secondary growth; nearly all are trees, and it is extremely doubtful 

 if the group ever contained herbaceous forms. They show rather 

 uniform xerophytic structure, due possibly to the character of the 

 water-conducting tissues, or to the evergreen foliage, since of the 

 existing species, only the bald cypress, ginkgo, the larch, and 

 Glyptostrous, are deciduous. They usually can not compete suc- 

 cessfully with angiosperms under genial conditions. Structurally 

 the bundles are collateral and a primary persistent cambium de- 

 velops all of the secondary tissues. The water-conducting tissues 

 are tracheids with bordered pits and true vessels are found only in 

 the Gnetales. Both mega and microspores are normally formed in 

 cones (strobili), which are never bisporangiate. 



The Araucariales and Taxales are dioecious, while the Coniferalcs, 

 Cordaitales, and Ginkgoales are monoecious. The sporophylls follow 

 the leaf arrangement and hence are spiral or cyclic. The stami- 

 nate cones have two or more sporangia to the sporophyll, hence 

 these are less numerous than in the Cycadophytes. They are exceed- 

 ingly variable and very characteristic for genera. The ovulate 

 cones are varied and their morphological interpretation has been 

 warmly debated for a century. A digest of the various opinions 

 advanced is given by Worsdell. (Annals of Botany, vol. 18, p. 57, 

 1904.) 



Pollination is effected through the agency of the wind (ane- 

 mophily). The stock is of great antiquity and contemporaneous 



