1907-1908.] Galls, Gall-makers, and Cuckoo Flies. 35 



have practised what is called caprification. This operation 

 consists in hanging up bunches of wild figs (Caprificus) upon 

 their cultivated trees (Ficus), that the flies which issue from 

 the former may enter their cultivated figs and fructify them. 

 These flies or fig-wasps are hatched in the interior of the wild 

 variety of fig. A fig, it may be necessary to explain, is a 

 hollow flower-stalk, in the interior of which the little blossoms 

 are developed. Each species of fig throughout the world 

 appears to be attended by its own particular species of fig- 

 wasp, and produces two varieties of fruit. At a certain period 

 the female insect enters the wild fig and inserts an egg into 

 the seed-vessel of each of its little flowers, with the result that 

 by -and -by the fruit, instead of seeds, contains a number of 

 galls. Erom these gall-flowers in due time the flies emerge, 

 but before escaping into the air they are plentifully dusted 

 with pollen from the male flowers growing near the opening 

 of the fig. Carrying this with them when they enter a fig of 

 the other variety, they fertilise its flowers ; but the latter 

 have a very long style which prevents the insects depositing 

 their eggs ; otherwise it is difficult to understand how any 

 fertile seeds could be matured. The fruits of the wild variety 

 are thus practically galls or wasp-nurseries, and this, taken in 

 connection with the exceptional structure of the fig, rather 

 favours the idea of flowers and galls being of kindred origin. 

 Here it should be mentioned, as highly favourable to Henslow's 

 views, that Dr Cunningham, having lately studied the process 

 of caprification in Ficus Eoxburgii at Calcutta, has arrived at 

 the startling conclusion that although the insects enter the 

 figs they carry no pollen ; but that by uselessly pricking the 

 ovaries, for they cannot penetrate them so as to lay eggs, they 

 induce not only a flow of fluid within the figs, but the irrita- 

 tion thus set up is actually the cause of the development of 

 embryos as buds outside the true embryo sac, in which no true 

 embryo is produced.^ There is quite a literature on caprifica- 

 tion, but evidently the last word has not yet been said upon 

 the subject. 



In this connection reference may be made to those curious 

 formations known as " domatia " occurring on certain plants 

 much infested by ants. Ants are believed to be responsible 

 ^ Henslow, ' Making of Flowers,' p. 109. 



