178 THE INSTABILITY OF LEAF-MORPHOLOGY, 



Since the foregoing was written, my attention has been drawn 

 by Mr. Maiden to a reference on this subject in "A Text-Book 

 of Botany," by Professors Coulter, Barnes, and Cowles, members 

 of the Botanical Staff of the University of Chicago (1910-1911). 

 In Vol. ii. of this work, which treats of Ecology, a chapter is 

 devoted to " Variation in Leaf-Forms," (p. 589) in which the 

 authors note the value of the determination of the causes under- 

 lying leaf-forms, in relation to specific distinctions, and {Joe cit.) 

 offer an hypothesis founded on species with an ancestral plas- 

 ticity and fixed descendants, or possibly (pp. 590-591) that some 

 forms have always been rigid and others always plastic. "Form 

 Variation in Amphibious Plants" is discussed (p. 593), and ex- 

 amples given, showing the wide range of variation obtaining in 

 the structure" of the aerial and water-leaves of this aquatic group. 

 Juvenile and adult leaves are considered (pp. 596-597) in relation 

 to ancestry, and the phenomenon of rejuvenescence, the latter 

 being regarded as an indication of a sudden shock which causes 

 the plant to return to a youthful stage. [An example of rejuven- 

 escence in Acacia florihxmda Willd., attributable to mechanical 

 injury, is given by the writer(13; 1914, p. 159), and a further ex- 

 ample in A.melanoxylon R.Br., in which the cause of the change 

 is not apparent (13; 1914, p.254)j. 



BIBLIOGRAPHY. 



I.Andrews, E. C. — "Development and Distribution of the Natural 

 Order Legiiminosfe. Journ. Proe. Roy. See. N. S. Wales, xlviii., 

 p. 333, 1914. 



2. Baker, R. T., & Smith, H. G. — Research on the Genus Eucalyptus, 



1902. 



3. Baker, R. T. — Description of Acacia diformis. These Proceedings, 



1897, p. 154. 



4. Bentham, G. — Flora Australiensis, 1886. 



5. Cambaoe, R. H. — Series of Papers on the Geographical Distribution of 



the Plants of N. S. Wales. These Proceedings, 1900-1913. 



P). " Development and Distribution of the Genus Eu- 

 calyptus." Presidential Address, Roy. Soc. N. S. Wales, 1913. 



7. "Acacia Seedlings." Part i. Journ. Proe. Roy. 



Soc. N. S. Wales, xlix., p.81, 1915. 



