BY A. A. HAMILTON. 163 



HALORAGE.E. 



Variation in the emerjced and submer2;ed leaves occurs in the 

 genus Myriophylhim. In both Haloragis ceratuphi/Jla Endl., 

 and //. heterophylla Brongn , leaf-division occurs, varying from 

 almost entire, to coarsely-toothed, and pinnatifid; and both are 

 irregular in the alternation of their leaves. 



MTRTACEiE. 



In the N.O. Myrtaceie, the genus Eucalyptus provides many 

 instances of leaf- variation. The attention concentrated on the 

 genus by leading .\ustralian botanists, who have specialised in 

 this syl vatic group, has resulted in a searching investigation of 

 their structure, from the cotyledon to the mature tree, and has 

 incidentally disclosed many examples of the difficulty of dis- 

 criminating between some of its members on leaf-characterisa- 

 tion. Bentham(4; iii , p.l86) says:— "The old division of the 

 genus according to the opposite or alternate leaves is now found 

 to be quite fallacious," and, loc. cit., " The extraordinary differ- 

 ences in the foliage of many species at different periods of their 

 growth add much to the oi'dinary difficulties arising from the 

 gradual transition of varieties, races or species, one into the 

 other." Again, (p. 187) " It appeared quite useless in any manner 

 to describe these sapling leaves in the several species where 

 they have been observed, for they present at once the greatest 

 similarity in the corresponding leaves of different species, and 

 the greatest dissimilarity in the different leaves of the same 

 species or specimens." J^aron von Mueller(22) notes several 

 instances, in his specific descriptions, of members of this genus 

 exemplifying the instability of leaf-morpholog}' as a termino- 

 logical factor. In his preface to (18), the author, considering 

 V^ariation in the Genus(p.6), offers some generalisations on the 

 modification of leaf-characters, and, in the already published 

 portion of this comprehensive work, has cited numerous in- 

 stances of similarity of leaves in opposing, and variation within 

 the compass of species, accompanied l)y plates showing difliering 

 forms of leaves. Modification of leaf-characters in £J. coricea A. 

 Cunn., referable to elevation (16; p. 35) are noted by the author, 



