Wall. — Ranunculus paucifolius T . Kirh. 101 



Zealand. The particular community here studied shows this with especial 

 clearness, consisting as it does of a small association of plants all of which 

 show very definite xerophytic adaptations, while some of them can exist 

 only under certain very special and peculiar edaphic conditions such as 

 may have obtained more widely in the past. The conditions governing 

 plant-life before and during this period of drought may be supposed to have 

 been much the same as those of the Sahara at the present time, thus 

 described by De Vries (after Battandier) : " Originally this region must 

 have had an ordinary degree of rainfall and moisture . . . Then . . 

 the rainfall must have slowly diminished, taking centuries ... to 

 reach the conditions which now prevail. The consequent changes in this 

 flora must have been correspondingly slow, and must have consisted mainly 

 in the disappearing of the larger part of the species ; first of those which 

 were dependent on the higher degree of moisture ; then of others ; until 

 at the present time only the most drought-resisting forms are spared " 

 (pp. 589-90). He proceeds to show that no specific changes, probably, 

 were brought about by this process ; that a large number of the species 

 of this arid region are monotypic genera, each genus consisting of a single 

 species ; whereas, " if there had been any degree of adaptation during this 

 whole period of increasing dryness, new species would have been produced 

 — from those forms which by their own inherent capacities wovild be the 

 very last to be threatened with extermination. These genera would there- 

 fore have produced quite a number of smaller or even of larger species, 

 adapting themselves more and more to the changing conditions and stock- 

 ing the desert, in the same way as other deserts have been stocked, from 

 adjoining countries! " As this has not happened, it is concluded " that the 

 single species . . . have not undergone any change in the direction 

 of drought-resistance, but have simply been those which happened to be . 

 the best fitted for the life in the desert. A thick epidermis, a small display 

 of leaves, long and deep roots, were the main qualifications for this 

 choice " (p. 590). 



Theh, in our case, we assume tliat the moister climate re-established 

 itself ; the mesophyte flora which had been destroyed here, but had main- 

 tained itself in some adjoining land where the conditions remained favour- 

 able, returned and gradually repeopled the desert or semi-desert, while 

 the xerophytes retreated before it to those places, such as shingle-slips 

 and areas like the small hollow at Castle Hill, where they had an advantage 

 and have subsequently maintained themselves. But, in contradistinction 

 to what has been said above, we must accept the following propositions 

 as to this community of plants :'- — 



(1.) The species here studied — e.g., Ranunculus paucifolius, Lepidiuni 

 sisymbrioides, Oreomyrrhis andicola var. rigida, and Poa acicularifolia — 

 all existed and held their own among the pre-drought mesophyte flora, 

 but no.t perhaps exactly in their present form, since " adaptations " are 

 not denied except as dift'erential marks of new species. The only alter- 

 native is that they have originated, some or all of them, since the period 

 of " drought." 



(2.) All these species must have had a high degree of plasticity, and 

 thus they are able gradually to accommodate themselves to the mcreasingly 

 severe drought ; but all must have had already, at the beginning of the 

 period, a definitely drought-resisting structure, and this was not at any 

 time acquired by any of them in response to any external stress, and it 

 wovild be at first quite useless to them. 



