CONIFERALES 337 



has been demonstrated in earlier pages that Paleozoic gymno- 

 sperms are characterized by the complete absence of parenchyma- 

 tous elements in the wood and at the same time by the general 

 absence of annual rings in the stem. Pinus, as regards the organ- 

 ization of the storage devices of the wood, is therefore clearly 

 allied with Paleozoic types such as the Cordaitales. 



There are other conditions, however, which indicate for Pinus 

 a primitive position among the Abietineae. First of all there is 

 the possession of short-shoots. Pinus in this feature of organiza- 

 tion presents a marked resemblance to the Ginkgoales, which 



FIG. 245. Microspores of Ginkgo and Abies 



also bear their foliar organs on special spurs or short-shoots. 

 Nor is the common possession of short-shoots unparalleled by other 

 significant characteristics. Ginkgo and the Abietineae strongly 

 resemble one another in the possession of bisporangiate sporo- 

 phylls. In the two groups there are two microsporangia and 

 two megasporangia or seeds on the reproductive foliar organs. 

 The view sometimes advanced that the ovuliferous scales in the 

 Abietineae consist of a fused pair of foliar structures has apparently 

 no evidence in its favor. It is as clearly a single leaf as is the 

 microsporophyll. The microspores in the Abietineae and in the 

 Ginkgoales also present striking points of resemblance which 

 have only recently been completely realized. In the monotypic 

 Ginkgo the pollen is winged as in the more primitive Abietineae 

 and resembles in its internal organization the structures found 

 in the microspores of that subtribe of conifers. Fig. 245 illustrates 

 the numerous features of internal and external resemblance between 



