84 Significance of Spines in Discaria Toumatou. 
which I observed in the shade of a subalpine Nothofagus forest, 
was quite twiggy and erect, still in fact, although fully grown and 
of considerable age, in the juvenile form. 1 The same may be 
observed in the equally xerophytic shrub Corokia Cotoneaster, 
Raoul, frequently a companion plant of the above Pittosporum. 
At 1200m. on Mt. Torlesse, a mountain in the dry eastern 
climatic region of the South Island, I have seen that comparitively 
leafless, and most rigid, low-growing shrub, Hymenanthera dentata, 
R.Br. var alpina, T. Kirk, whose branches “ usually terminate in a 
stout spine,” 2 where sheltered from the sun and wind against a 
rock, put forth semi-hygrophytic reversion shoots. Finally, leaving 
out of the question other striking cases, Aristotelia fruticosa, 
Hook, f., when growing in extreme xerophytic stations, has no leaves 
on its external branches, which at their exposed extremities become 
spine-like and almost pungent. 3 
From the above, there seems to be sufficient evidence to show 
how an organ so specialized as a spine may be directly caused by 
exposure to xerophytic conditions. 
When discussing elsewhere 4 the history of the floras of the 
small outlying New Zealand islands, I have gone, though at no 
great length, into the bearing which this question of differences 
between hygrophytic juvenile and xerophytic adult forms of certain 
New Zealand plants has on the matter of former land extension of 
New Zealand. Suffice it to say here, that from the teaching of 
geology, 5 it has been concluded by Diels 6 that in the east of 
“Greater New Zealand” there was in all probability a steppe or 
semi-desert climate, which would insist on xerophytic adaptations 
being acquired by such plants as were to successfully cope with 
their new surroundings,—just the climate, in fact, with which 
Discaria Toumatou , Aciphylla Colensoi and many other New 
Zealand xerophytes would be more in harmony, than with the one 
to which they are at present exposed. According to this view, 
hygrophytic juvenile forms, such as the Discaria here figured, 
and the species of Veronica referred to above, may without 
> Trans. N.Z. Inst., Vol. XXXIII., p. 266. 
2 T. Kirk. The Students’ Flora of New Zealand and the Out¬ 
lying Islands., 1699, p. 44. 
3 See plate 18. Trans. N.Z. Inst., Vol. XXXVI., 1904. 
“ Trans. N.Z. Inst., Vol. XXXIII., pp. 277-282, and Vol. XXXVI , 
p. 317. 
6 F. W. Hutton. The Geological History of New Zealand, Trans. 
N.Z. Inst , Vol XXXII , pp. 173-178, and p. 182. 
* loc. cit., pp. 296-8. 
