FLORA OF THE HAWKESBURY SANDSTONE. 221 



leaves are absent, while there are other cases where both leaf forms 

 are present on the same plant. The last case has probably no 

 •epharmonic significance, but in the xerophytic Anisoionie filifolia^ 

 (Umbelliierfe) the effect of a change of environment is very striking. 

 This species when growing on subalpine shingle-slip has much cut 

 filiform leaf-segments. These in the seedling are much broader,^ 

 but the plant also grows under mesophytic conditions, in which 

 ■CcLse the seedling form persists, although the plant flowers freely. 

 This last case is the strongest, so far as the cases given in this 

 paper go, in support of a possible ontogenetic origin of certain 

 species, since the question of a reproduced ancestral form, which 

 -could with much reason be argued for most of the former examples, 

 may be here put on one side, the relation between breadth of leaf 

 and variation in aridity of station being so well marked. 



2.— THE XEROPHYTIC CHARACTERS OF THE FLORA OF THE 

 HAWKESBURY SANDSTONE. 



By A. G. HAMILTON. 



The general aspect of the flora of the Hawkesbury sandstone 

 is very characteristic. Wherever that formation occurs, even 

 in detached outliers, the flora can be recognised at a glance. The 

 plants are shrubby and small, very twiggy, the leaves hard and 

 leathery, and there is a general scragginess which is unmistakeable. 

 Schimper^ sums up the characters of xerophilous plants as 

 below : — 



1. — Reduction of leaf surface. 



2. — Diminution of intercellular spaces. 



3. — Augmentation of vessels and sclerenchyma. 



4. — Increased length of palisade cells. 



5. — Increased thickness and amount of cutin in the outer 



walls of the epidermis. 

 6. — Sinking of the stomates. 

 7. — Increased number of air-containing cells. 

 8. — Supply of water-storing cells. 

 He also mentions wax and other protective substances on the 

 ■surface of the leaves, hairiness, thorniness, and the power of altering 

 the position of the pinnae in the pinnate leaved plants. 



Henslow^ mentions in addition the secretion of ethereal oils, 

 tannin and certain hygroscopic salts as features in xerophytes. 



Almost all these characters appear in the plants of the Hawkes- 

 bury flora, and in most instances several of them are found in the 

 same plants. They are particularly noticeable in the endemic Aus- 

 tralian plants ; indeed I think it would be safe to say that every 

 one of these exhibits one or more of the xerophilous structural 

 characters. 



1. Anisoto>ne fiUfolia (Hook, f.), Cockayne comb. nov. — Ligusticum filifolium Hook, f., in " Handb. 



N.Z. Flora," p. 95, 1864. 



2. See Cockayne, Trans. N.Z. Inst. 33; fig. 38, pi. 12. 



