74 A NEW ZEALAND NATURALIST'S*CALENDAR. 



native mammals (except bats, etc.), that such devices 

 would be almost unknown among the plants. It is accord- 

 ingly a curious fact that there is not a single endemic 

 species that is, a species confined to these islands which 

 is dependent on this mode of distribution, except, perhaps, 

 one or two feeble sedges. The example which naturally 

 suggests itself is the familiar piri-piri usually mis- 

 pronounced bid-a-bid (Accena sanguisorbce), so much 

 appreciated by picnickers. This plant is a degenerated 

 representative of the Rose family, and its device consists in 

 having its calyx-lobes developed into four spines, which, a 

 little before the fruit matures produce at their tip a small 

 spreading barb. It is a most perfect anchor, and the way 

 in which it can attach itself to cloth would be very interest- 

 ing if it were not so irritating. Now it is noticeable that 

 of the five* species which occur in these islands only two 

 have the barbs of these the one commonly found here is 

 equally abundant in Tasmania and Australia. There it 

 probably developed its barbs to catch the fur of kangaroos, 

 wombats, and similar animals, and was perhaps introduced 

 into New Zealand by means of birds. The other species, 

 which occurs more commonly in the upland districts of this 

 island, is evidently a form of great antiquity, as it ranges 

 away to Tierra del Fuego and the Falkland Islands. Thus 

 the two species which have a wide distribution outside of 

 New Zealand have the barbs, while the other three, which 

 appear to have originated in these islands and are confined 

 to them, have lost the barbs ; in one of them even the calyx 

 spines are scarcely developed. Thus a structure which was 

 functionless because useless, where there was nothing to 

 catch on to, has evidently tended to disappear. 



* Cheeseman describes six species of Ac&na, but of these A. Nov<e- 

 Zealandia is so closely allied to A. san%uisorb<e that it hardly deserves 

 specific rank. 



