250 



Dr. A. Arber. On the Development and 



a century ago, A. P. de Candolle* pointed out that the young leaves of 

 Palms are entire, and that it is only subsequently that they become torn 

 into thongs (" dechirees en lanieres ") ; the segments are thus merely pseudo- 

 lobes (" pretendus lobes "). De Candolle emphasises the fact that, though 

 the idea of cutting (" decoupure ") enters so largely into the technical 

 language of leaf-description, it is only to the Palms that such terms can be 

 applied with literal exactitude. 



Subsequent workers have carried back our knowledge of Palm leaves to 

 the earliest stages in their developmental history. Von Mohl.f Karsten,J 

 and Trecul,§ in the middle years of the nineteenth century, followed the 

 course of their entogeny, and attempted to trace the stages passed through 

 by the leaf-rudiment between its origin and that curiously plicate phase 

 which is succeeded by the ultimate subdivision into separate segments. 

 About forty years later, the subject received renewed attention, principally 

 from Eichlei'H and Naumann;1F the work of Eichler remains, even to the 

 present day, the standard account of the development of Palm leaves. 

 More recently, Deinega** and Hirmerff have returned to certain aspects 

 of the question which the earlier workers had left in some obscurity. 



A study of the literature shows that, though there is essential unanimity 

 as to the manner in which the simple leaf-limb splits into its ultimate 

 pseudo-compound form, there are, on the other hand, marked differences 

 of opinion about the history of that early developmental period vjhich precedes 

 the actual subdivision of the leaf. All workers are agreed that, at an 

 extremely early stage, the upper part of the leaf-rudiment shows a series 

 of deep furrows alternating with ridges, which give it an apparently plicate 

 form. But authorities differ as to the mechanism by which this plication 

 is brought about. One school has maintained that there is actual splitting 

 of the leaf-tissues (von Mohl, Trecul, Naumann), while others hold that only 

 folding takes place (Karsten, Eichler, Deinega, Hirmer). The discussion 

 of these conflicting views will be postponed until after I have described my 

 own observations on the ontogeny of the Palm leaf. 



* Candolle, A. P. de (1827). 

 t Mohl, H. von (1845). 

 % Karsten, H. (1847). 

 § Tr6cul, A. (1853). 

 || Eichler, A. W. (1885). 

 H Nauruann, A. (1887). 

 ** iJeinega, V. (1898). 



t+ Hirmer, M. (1 919) ; see this paper for further references. 



