24 SCIENCE FROM AN EASY CHAIR 



on bits of floating wood or of pumice-stone, and some on 

 one another ! They are all hermaphrodites, but Darwin 

 found in several a most singular thing, namely, the exist- 

 ence of minute males, complemental to and parasitic on 

 the hermaphrodites. His discovery was doubted and 

 denied, but he had the pleasure of seeing it at last fully 

 confirmed thirty years after his book on cirrhipedes was 

 published. 



Darwin discovered that the presence of the same 

 species of plants and of some few animals on distant 

 mountain summits and in the Arctic region is due to 

 the former extension of ice between these situations 

 during the last glacial period. He was, before every- 

 thing else and by necessity for the examination of his 

 theory, a geologist, and wrote many valuable geological 

 memoirs. The history of the origin of the species of 

 living things consists largely in tracing them to extinct 

 creatures, and in showing what were the possible migra- 

 tions and what the conditions of land and water, tempera- 

 ture and vegetation, in past periods, and in regard to 

 given areas of the globe. The book on the Fertilisation 

 of Orchids was the first published by Darwin after the 

 Origin of Species. In it he showed how the marvellous 

 shapes and colours and mechanisms of the flowers of 

 orchids are adapted to ensure cross-fertilisation by insects, 

 and how they can be explained as originating by the 

 natural selection of variations if the value of cross- 

 fertilisation is once recognised. The explanation of the 

 reason for the existence of two kinds of primrose flowers 

 the short-styled and the long-styled clearly arrived 

 at by him as being a mechanism to secure cross- 

 fertilisation, delighted him in 1862, and led him to 

 discover the same sort of modification in other flowers. 

 Then, in 1864, he published his researches on Climbing 

 Plants, and later a book on the Movements of Plants, in 



