30 



EDWARD C. JEFFREY ON 



order two or three prothallial cells are formed within the germinating pollen grain 

 previous to anthesis, as has been shown by Strasburger and others in the case of Larix, 

 Pinus, Tsuga, etc. In the Cupressineae, using the term in the broader sense to include 

 such forms as Sequoia and Taxodium as well as Thuja, Cupressus, and Juniperus, 

 this is not the case as only the stalk and antheridial cells and the tube nucleus make 

 their appearance in the germinating microspore. It may be urged that the winged 

 pollen, found in Pinus, Abies, Cedrus, Picea, etc., is to be regarded as a mark of high 

 specialization and as a consequence an indication of a modern origin for the group under 

 discussion. This is by no means necessarily the case, for examples of winged micro- 

 spores are known to have existed among the Lepidodendrids (Scott, '98), and there 

 are no cases of winged pollen grains among anemophilous Angiosperms, which may 

 be taken as the most modern type of wind-fertilized vascular plants. It seems probable 

 that the air sacs are for the purpose of reducing the specific gravity of the ancestrally 

 heavy and multicellular type of pollen grain found in the Abietineae. 



Perhaps the most important indication of the primitive nature of the Abietineae 

 is supplied by the study of their leaf trace. It is now a well established general prin- 

 ciple that ancestral features are apt to persist for a long time in the vegetative leaves 

 of the vascular plants. This principle is, for example, very well illustrated by the 

 case of the Cycads, referred to in an earlier paragraph. Attention has been called 

 in the descriptive part of this memoir to the fact that no matter what may be the 

 character of the foliar strand in the lamina of the leaf in the Abietineae, it is always 

 a double strand in the cortex. A double leaf trace was characteristic of Lyginoden- 

 dron, Poroxylon, Calamopitys, the Cordaites, and others of the fossil and transitional 

 Gymnosperms. It is also exemplified in the foliar trace of Ginkgo and in the double 

 strand, which often passes off to the sporophylls in the Cycads. Scott (:00) has called 

 attention to this feature of the older Gymnosperms and suggests that it may have 

 a taxonomic value. In view of the facts described in this memoir for the Abietineae, 

 the double trace appears to have a peculiar significance, especially when it is recalled that 

 the Cupressineae have but a single foliar strand (Bertrand, 74) . The topography of the 

 double foliar trace in the Abietineae is such that we may regard the single leaf trace, 

 which is found in what we believe to be the less ancient orders of the Coniferales, i. e., 

 the Cupressineae, Taxineae, etc., as originating by the progressive reduction in size of 

 the leaves. The process is centripetal, that is, it progresses from the apex of the leaf 

 downwards into the cortex of the stem, so that starting with a single bundle in the foliar 

 apex we arrive sooner or later at the primitive double bundle. The separation may take 

 place high up in the lamina of the leaf, as has been pointed out by Strasburger ('91) 

 in the case of Pinus. Further, in very small leaves of the Abietineae, as has been noticed 



