SURVIVALS AMONG PLANTS OF THE PAST. 



309 



known in Far Eastern regions, closely resembles the fossil PtijclLO- 

 carpiis. 



Between the spore-bearing Cryptogams and true seed plants or 

 Gymnosperms were the fossil Pteridosperms — i.e. " Fern-seed plants," 

 which combine the characters of both classes. These were plants 

 resembling ferns in th,e foliage, and were therefore supposed to belong 

 to that group, until the reproductive organs were found attached to 

 the fronds. They, however, bore ovides and seeds resembling those 

 of Cycas. The stamens, however, were nearly " peltate " and find 

 resemblances in several existing genera, as Zamia, Taxiis, Araucaria, 

 &c., as well as the sporangia of horsetails. 



We now come to the seed plants. The difference arose by the 

 macrosporangia having only one instead of many macrospores, and that 

 one forming an ovule, provided with one coat (the secimdine) only. This 

 was prolonged into a tubular or inverted funnel-shaped process, the 

 broad base being callecl the pollen-chamber, as the pollen fell into it. 

 The earliest kind of pollen-chamber was formed by the 7iucelhis of the 

 ovule itself, and this is still the case in Cycas and Ginkgo. The micro- 

 sporangia, on the other hand, constituted the anther, the microspores 

 becoming pollen-grains. 



Gymnosperms, which arose in the Coal period, are now represented 

 by three families only — Cycadeae, with nine genera, Chietaceae, with 

 three, and Coniferae, divided into six tribes and thirty-one genera. One 

 tribe, Taxeae, has six genera, of which Taxus, the yew tree, and the 

 Gi7ikgo of Japan are survivors from the distant past. 



A very common feature of the earliest as well as of surviving genera 

 is the presence of catkins, consisting of bracts closely arranged on an 

 axis, with or without stamens or ovules in their axils, but in Angio- 

 sperms there are, of course, pistils. Such is the characteristic feature 

 of many living trees, which are also presumably survivals, from the 

 paucity of the genera in their families respectively, as is seen in the 

 Amentiferae — i.e. " Catkin-bearers " — as well as in Myrica and 

 Casuarina, sole existing representatives of their families, both of which 

 are therefore doubtless primitive types. 



Though it is customary to say that Gymnosperms have no carpels 

 or pistils, authorities differ on this point, for the latest view regards 

 a not infrequent presence of an imperfect integument outside the ovule, 

 mostly free from it, as the pistil ; but in all cases it remains open above, 

 so that the ovule has to receive the pollen directly within the pollen- 

 chamber. Whatever be the origin of the pollen-chamber, it occurs in 

 all living Gymnosperms. 



A characteristic feature of the fossil Cordaianthus, and several 

 Gymnosperms still living, as well as of the Avientiferae, is to have the 

 anther-cells borne singly, and not coherent in pairs, as usually prevails 

 in stamens. 



Perhaps this want of cohesion between the two pollen-sacs of the 

 anther may have been a result of the primitive and prevailing feature of 

 dichotomy of the ribs and veins in leaves, as seen in the frequently lobed 



