CONIFERAE. 63 



gradually dies out and from which the parallel nerves emerge and afterwards 

 branch, but chiefly because the leaf-stalk is deeply channelled, and when 

 well preserved shows a basal swelling above the smooth plane of separation. 

 Heer was afterwards confirmed in the happy idea of comparing them with 

 Ginkgo by finding seeds on the same slabs from Spitzbergen which reminded 

 him of that genus, together with short bits of branches thickly beset with 

 roundish scars which he compared to the short shoots of Ginkgo. It was 

 important also that similar objects were found associated with Ginkgo-like 

 leaves in other localities also in the polar zone, and with the further addition 

 of male flowers also resembling those of Ginkgo. From all this we may 

 with Heer consider it as proved that these leaves cannot be the leaves of 

 ferns ; the present view of them it is true rests chiefly on a conclusion from 

 the association together of leaves, seeds and branches, which does not give 

 absolute certainty, though it appears to be better founded in this case than 

 it is in any other in the older formations. Heer l says that the nervation in 

 his forms resembles that in our Ginkgo, but this does not appear from the 

 figures, for there the nerves which are of equal strength simply diverge and 

 spread from the base of the leaf, and there is no sign of the two chief strands 

 which run along the lower leaf-margins and send branches into the leaf- 

 lobes. Heer also states that Baiera pluripartita, Schimp. from the Wealden 

 is so closely allied to his Ginkgo digitata that it must be placed in the same 

 genus, but I am not so certain of this, because, after examination of the best- 

 preserved specimens of the form from Osterwald in the Deister country in 

 the Gottingen collection. I have satisfied myself that the nervation is some- 

 what different from that of Ginkgo. It is however very different even with 

 the best material at one's disposal to get a clear view of the course of the 

 nerves, especially close to the stem, which is the chief point, because the 

 interspaces between them are here very small and the thickness of the strip 

 of coal and the transverse corrugation of the surface, which I should take 

 with Heer to be an original character of the leaf, come in the way and 

 prevent an exact determination. In the same work, and in the next section, 

 which is on the Jurassic flora of Eastern Siberia, Heer on the strength of 

 the view once gained has gone a good deal further by adding several species 

 to the genus Ginkgo as he conceives it, and associating with it a number of 

 genera, more particularly Baiera, F. Braun, in an amended form. His work 

 and that of Schenk should be consulted for further species of Ginkgo from 

 the Chalk of Greenland and from Eocene and Miocene strata. One of the 

 Miocene forms, G. adiantoides, Heer, found at Sinigaglia is closely allied to 

 the living species. Heer illustrates the genus Baiera, from which he had 

 removed several of the older species in order to put them under Ginkgo, 

 chiefly from Baiera longifolia, Heer, which occurs abundantly in the Lower 



1 Heer (5). 



