THE VARIETIES OF FERTILISATION. 315 



and Umhelliferce ; as well as are those dependent upon tlie 

 wind, which never fails, such as Willows, Cyperacece, and 

 Grasses. On the other hand, all regularly self-fertilising 

 plants are abundant, and, trogether with certain wind- 

 fertilising plants, are cosmopolitan. 



Although the idea that self-fertilisation is injurious is 

 certainly not held now by botanists in so absolute a form as 

 Mr. Darwin often stated it, yet it will not be amiss to point 

 out the want of agreement between his conclusions and his 

 own experiments. 



In a chapter on " General Results," * he commences by 

 saying : " The first and most important of the conclusions 

 which may be drawn from the observations given in this 

 volume, is that cross-fertilisation is generally beneficial, and 

 self-fertilisation injurious. This is shown by the difference 

 in height, weight, constitutional vigour, and fertility of the 

 offspring from crossed and self-fertilised flowers, and in 



structure of the flowers ; first, in being adapted to a great variety of 

 insects. Thus, on ten species of plants, Miiller detected 546 species of 

 insects, in the following proportions, Lepidoptera, 15 p.c. ; Apidse, 41 

 p.c. ; Diptera, 27 p.c. ; other short-tongued insects, 17 p.c. Bees, 

 therefore, are the chief visitors. This is almost invariably the rule : the 

 only species mentioned by Miiller in his table in which short-lipped 

 insects surpass in number the Apidge is Chrysanthemum leucanthemum, 

 which has a corolla tube, 3 mm. in length, in which the honey rises 

 up into the widening throat and is easily accessible. The number of 

 Lepidoptera is in the proportion of 6-9 p.c. ; Apidae, 16*6 p.c. ; Diptera, 

 38-9 p.c. ; others, 37"5 p.c. In Achillea Millefolium, with a corolla tube 

 of 3 mm., Lepidoptera are 6-9 p.c; Apidaj, 34*5 p.c; Diptera, 24-1 

 p.c, and others, 34*5 p.c. Lastly, in Centaurea Jacea, with a tube of 7 to 

 10 mm., the Lepidopf?era rise to 27 p.c. ; Apidae, 58*7 p.c ; while Diptera 

 sink to 12-5 p.c, and other short-lipped insects are only 2 p.c. 



The Compositce thus well illustrate the fact that tubes are propor- 

 tionate in length to the more specialized insects, a universal feature 

 seen in all other orders as well. 



* Cross and Self Fertilisation of Plants, p. 436. 



