Botany. 497 



The suggestion of Professor Bower that the general term Fhyl- 

 lopodium be introduced to designate the central portion of the 

 framework of the leaf appears to be well-advised, and in the case 

 mentioned would remove all ambiguity. 



It remains to say something relative to one of the cases cited 

 by Balfour, namely the species of Eucalyptus, which he adduces 

 as illustrations of Phyllodia. These are not flattened pecioles, 

 but are true leaves with a well-marked twist, which in some in- 

 stances is so great as to give to them a vertical aspect. This 

 twisting was observed long ago by Robert Brown (Misc. Works, 

 Ray Society, vol. i. p. 62), who says : " They (that is, Acacia and 

 Eucalyptus), agree very generally also, though belonging to very 

 different families, in a part of their economy which contributes 

 somewhat to the peculiar character of Australian forests, namely, 

 in the leaves or the parts performing the functions of leaves 

 being vertical or presenting their margin and not their surface 

 towards the stem ; both surfaces having consequently the same 

 relation to light. This economy which uniformly takes place in 

 the Acacise, as in them the result of the vertical dilatation of 

 foliaceous footstalk, while in Eucalyptus, where, though very 

 general it is by no means universal, it proceeds from the twist of 

 the footstalk of the leaf." 



Allusion must now be made to a conviction which has been 

 deepening in the mind of the present writer, that the vertical 

 Phyllodia of Acacias, and the vertically twisted leaves of Myr- 

 taceae are correlated with the so-called " sleep positions " of 

 leaves, whereby the amount of surface exposed to direct loss of 

 heat at night is materially lessened.* 



Such, I venture to suggest, may be regarded as permanent 

 sleep positions.f Comparison of the vertical Phyllodia with 

 those which lie in the plane of ordinary leaf-blades, indicates that 

 the latter belong to plants which, like the South American species 

 of, Oxalis, grow in shaded places, and are therefore more or less 

 sheltered from direct loss of heat by radiation. The information 

 which can be gathered from various authors, in regard to the 

 different species of Eucalyptus in which there is conspicuous ver- 

 tically through the twist at the base, indicates that here also we 

 have a kindred adaptation. But the facts thus far accessible in 

 regard to the different species with respect to this point are too 

 meagre to enable me to regard this as more than a suspicion 

 which will repay further investigation. The writer will welcome 

 any information bearing on the degree of verticality presented 

 by the leaves of all Myrtaceae, and on the climatal surroundings 

 of the different species. G. l. g. 



* It must not be overlooked that the vertical position has perhaps more ex- 

 tended relations to the loss of moisture during the day. 



f Compare Darwin. The Power of Movement in Plants, Am. Ed., p. 328. 



