162 TEST CASES [ch. xiii 



the characters become, and the less functional value do they 

 have, as is universally admitted. This test is entirely against 

 natural selection, even if it do not specially favour differentiation. 



TEST CASE XXXIII. RELATION OF MONOCOTYLEDONS 



TO DICOTYLEDONS 



A feature in geographical distribution to which Hooker called 

 attention in 1888, and Avhich was never explained until Age and 

 Area gave the key to it, is described in the following quotation 

 (18): "The conditions which have resulted in Monocotyledons 

 retaining their numerical position of one to four or thereabouts of 

 Dicotyledons in the globe and in all large areas thereof are, in the 

 present state of science, inscrutable." The exactness of the rela- 

 tion is remarkable. The latest figures in the writer's possession 

 add up to 36,639 species of Monocotyledons and 145,718 of 

 Dicotyledons, or almost exactly one to four. 



So long as one keep to large areas, and to the centre of the land 

 masses, the relation keeps wonderfully steady, but when one 

 comes to the edges of vegetation, especially to the north or to the 

 south, one finds fluctuation beginning, as also in the tropical belt 

 from Malaya (which has 26 per cent of Monocotyledons) through 

 Ceylon (27 per cent). While the average proportion is just 20 per 

 cent, and in the Kermadec Islands north of New Zealand is 21 per 

 cent, it is 31 per cent in the Chatham Islands to the east of New 

 Zealand, and 45 per cent in the Aucklands to the south, and again 

 26 per cent in Juan Fernandez and 30 per cent in Tasmania, all 

 these figures suggesting that the old southern continent was a 

 great home of Monocotyledons. In Europe there is a belt of high 

 proportion of Monocotyledons from Sardinia through France and 

 Britain to Iceland. In the Canaries the proportion is only 15 per 

 cent. 



Now there is no " monocotyledonous " mode of life to which 

 this group can have been adapted. Every kind of life is repre- 

 sented, and there is nothing in common in mode of life between 

 such things as orchids, grasses, lilies, aloes, bulrushes, water- 

 soldiers, palms, aroids, duckweeds, rushes, Bromeliads, yams, 

 bananas, gingers, etc. The steadiness of the proportion of Mono- 

 cotyledons to Dicotyledons goes to show that in their dispersal 

 adaptation played but a small part, and that it was primarily 

 governed by the laws of age and area, as is demanded by the 

 theory of differentiation. 



