CH. XV] ENDEMISM AND DISTRIBUTION: SPECIES 155 



show the numbers that occur in each zone of 100 miles from 

 north to south in the two large islands : 



Wides 33 3 4444444 



Endemics - 2 3 5 7 11 12 18 18 10 



If instead of taking the distribution in this way by zoning, one 

 take the actual longitudinal range of the different species, one 

 finds that of the 28 endemic Ranunculi, 10 have a range not 

 exceeding 60 miles longitudinally in New Zealand, while of 

 ranges 120, 180, 240, etc., there are only 1, 3, 1, 2, 4, 1, 1, 1, 2, 

 0, 1, 0, 1. The great bulk are obviously crowded towards the 

 short ranges. If one make five groups, occupying ranges from 

 0-200, 200-400, 400-600, 600-800, 800-1000 miles, one finds 

 that they contain 14, 7, 5, 1 and 1 species respectively. If, now, 

 one plot these figures in a curve (fig. on p. 162, curve 7), 

 one obtains a curve which is concave upwards, or what we may 

 term a hoUoiv curve. This type of curve we shall presently see to 

 be almost universal in distribution — and it proves of late to be 

 equally so in evolution itself. At first, perhaps, its presence will 

 not be readily noticed, but when one finds the figures for any 

 example of distribution or evolution showing a great accumula- 

 tion at one end, and the first two or three descending very rapidly, 

 while the remainder tend to taper away gradually, one will 

 generally find this type of curve shown, on actually plotting the 

 figures. It shows very strikingly in many of the examples 

 described below, e.g. the distribution of the Hawaiian endemic 

 species of CijHandra described on p. 160, (same fig. curve 6). 



Or one may take such a genus as Epilohium in New Zealand 

 (37, p. 171). E. jmrpiiratum is confined to the Alps of Otago, 

 4000-6000 feet, E. brcvipes to the northern half of South Island, 

 E. crassum to the greater part of the length of South Island; 

 E. melanocaulon ranges the whole length of South and the southern 

 half of North Island, E. microphyllu7n ranges yet farther north, 

 E. glahellum farther again, while E. rotundifoUum ranges the 

 M-hole length of both islands, and reaches SteA^art and the 

 Chathams. E. nummulari folium reaches all this, and also Auck- 

 land and ]\Iacquarie Islands to the south, while E. jmllidiflorum 

 ranges this and reaches Australia and Tasmania. Tins, or some- 

 thing like it, is the common type of distribution in New Zealand. 



If we take a genus— and there are many— that has no wides 

 in New Zealand at all (cf. p. 95), we find the same thing shown, 

 as, for example, in Gunnera (fig. on p. 158). Here there is one 



