41 



It had been hoped that similarity in development might serve 

 as an aid in the identification of fossil leaves of the forms dis- 

 cussed. That is to say, if the fossil pinnate leaf did not develop 

 in a manner similar to its nearest living relative, it would furnish 

 a warning to review the identification. Goebel,* however, states 

 that "... the course of development in nearly allied plants 

 varies, for example, in pinnate leaves it is sometimes acropetal 

 and sometimes basipetal." It is, however, suggestive that in 

 two of the cases here noted, Negiindo and Sapindus, the lobing of 

 the terminal leaflet was first noticed in the fossil species and that 

 this resulted in a successful search for similar examples among 

 the related living forms. 



The unsymmetrical outline of certain terminal leaflets from 

 which a lobe has split, such as is well shown in the terminal 

 leaflet on pi. B, fig. i, a, does, however, offer a suggestion to 

 those engaged in identifying fossil leaves. Should such a fossil 

 leaflet, minus its lobe, be preserved alone, the tendency would 

 likely be to regard it as a simple leaf, rather than as a leaflet 

 of a compound leaf. Hence, in endeavoring to determine the 

 probable relationship of any such unsymmetrical leaf, it might 

 be advisable to consider whether or not it could be a leaflet of a 

 compound leaf. 



Briefly then the leaves under discussion show: (i) that like 

 forms of leaves, of arrested development, occur in certain species 

 of living and fossil plants of the same genus ; (2) that these forms 

 indicate that similar methods of leaf development took place in 

 each of them; (3) that if "nearly allied" plants may develop 

 their leaves in different ways, it follows that the mode of develop- 

 ment is of questionable value to paleobotanists in identifying 

 forms of arrested development among fossil pinnate leaves; (4) 

 that in identifying simple fossil leaves of the form of the terminal 

 shown on pi. B, fig. i, a, if the lobe were not preserved, it might 

 be advisable to view it as a possible leaflet of a pinnate leaf. 



* Organography of Plants, authorized English edition, pt. 2, p. 330. 1905- 



