1884. 47 Trans. N. Y. Ac. Sci. 



striking exceptions in the broad leaves of Gittgko and Phyllocladus. 

 On the other hand Ephedi-a, Ulce many other desert plants, is almost 

 without leaves. In the ferns and umbellifercC also we find the foliage 

 very much dissected, almost as much so as that of aquatic plants — 

 why, no one has yet given us a reason. 



It has been suggested that the earlier forms of leaves were simple, 

 and that they have become compound by variation in descent. The an- 

 cient history of plants, which I have studied with much interest, gives 

 no support to such a theory. The groups of terrestrial plants which 

 earliest assumed importance were the conifers and the lycopods, but 

 they have retained practically the same forms of foliage from the 

 earliest times to the present ; the living Lycopodiiun doidroideiini be- 

 ing almost an exact copy in miniature of the Lepidodendra of the Coal 

 Measures, while the Mesozoic and Palaeozoic conifers exhibit the same 

 scaled or acicular leaves that characterize the most abundant conifers 

 of the present day. The Gingkos of the Mesozoic age generally had 

 more divided leaves than the Salisbitria of the Tertiary and present 

 times ; but on looking over the entire field, it is impossible to detect 

 any progressive tendency to simplicity or complexity in the foliage of 

 the coniferae. The cycads, of which the golden age was the Jurassic, 

 have always been characterized by pinnate fronds with often narrow 

 pinnules ; but their first development was in the Coal flora in the form 

 of Cordaites and Noeggerathia, in which the leaves were broader than 

 in most later species. 



The monocotyledonous plants, the grasses and palms, the yuccas 

 and pandanus, have, as a general rule, narrow leaves and a parallel 

 nervation, for which no adequate explanation has been offered ; while 

 some of the lilies and most of the arums have broad leaves of a 

 totally different structure. 



The broad-leaved angiosperms begin in the Cretaceous, and speedily 

 acquire pre-eminence in the vegetation of the globe. We now have 

 the life history of this group pretty well outlined in the elaborate 

 figures and descriptions of the Cretaceous and Tertiary floras, but we 

 look here in vain for any law of development in leaf-forms. Among 

 the earliest plants are the magnolias, remarkable for the simplicity of 

 their leaves, their entire margins, and their camptodrome nervation. 

 With these are oaks, generally with toothed, but only later cut and 

 lobed leaves ; willows, with simple leaves like those of the present 

 day ; Liqiiidambar , with species in the Cretaceous and Tertiary, hav- 

 ing leaves with broader lobes than the living one, and yet not decidedly 

 different ; Aralias, with digitate leaves, and Flatanus and Sassafj-as, 

 with broadly lobed leaves, were conspicuous elements in the earlier 

 angiosperm flora, but they were essentially what their representatives 



