T. D. A. Cocker ell — Descriptions of Tertiary Plants. 



77 



There is a variety known as decurrens Koehne, in which only 

 three to five of the upper leaflets are connate in a terminal 

 lobe, which, like the separate leaflets, is decurrent at the base. 

 Another variety is S. hybrida var. neuill/yensis (Dippel), 

 (Pyrus neuillyensis Hort.), of garden origin, having about 

 four pairs of separate leaflets, those of about the apical third 

 connate, but the leaflets not at all decurrent at the base. 



A related hybrid is Sorbus thuringiaca (Use) = Pyrus 

 thuringiaca Use, with shorter leaves, as might be expected 

 from the parentage, S. aucuparia X aria. In the fossils, the 

 characters of these hybrids are reproduced with astonishing 

 exactitude. The more common form is similar to S. hybrida, 



Fig. 1. 



Fig. 2. 



Fig. 1. — Sorbus diversifolia. 



Fig. 2. — Sorbus nupta. 



but narrower, and as in var. decurrens, the divisions are 

 strongly decurrent at the bases, so much so that the leaflets are 

 not wholly separated. In a form which I collected at Station 

 14 (fig. 1), the lobing extends far toward the apex of the leaf. 

 The form of the petiole, as well as the structure of the blade, 

 is extremely similar in the fossil and recent leaves. Being 

 thus wholly convinced that Sorbus diversifolia is a hybrid, I 

 naturally sought for the parents. It was necessary to find in 

 the shale species of the compound-leafed or Aucuparia type, 

 and also the dentate, or slightly lobed Aria type. The first 

 has already been published as Sorbus megaphylla Ckll., Bull. 

 Arm Mus. Nat. Hist., 1908, p. 95, pi. ix, f. 29. The second, 

 at first regarded as a mere variety of S. diversifolia, may be 

 described as follows : 



