36 Galls^ Gall-makers, and Cuckoo Flies. [Sess. 



for the remarkable growths in Myrmecodia and Hydnophytum, 

 and not only so but to have become indispensable to the 

 healthy development of the plants themselves. The pitchers 

 of Dischidia, which, like stipules of Acacia sphserocephala, are 

 greatly frequented by ants, also appear to be of the nature of 

 domatia. These peculiar growths occur in members of the orders 

 Rubiacese, Myristicaceae, Euphorbiacese, Verbenacese, Melasto- 

 macese, and Palmse ; intricate galleries are also constructed by 

 certain species of ants in the rhizomes or underground stems of 

 one or two ferns, which have become much modified in conse- 

 quence.^ It is asserted that the habit of producing domatia 

 is now hereditary, without the actual presence of the insect.^ 

 If, as is generally supposed, these ant-plants benefit by the 

 presence of the ants, and are by them defended against the 

 attacks of their enemies, then the domatia, though originally 

 growths induced by the activity of the insects themselves, may 

 be regarded as quarters provided by the plants for their ant 

 garrisons. 



Some of the statements given above regarding the suscep- 

 tibility of vegetable tissue to external stimuli recall the story 

 of Aladdin's lamp in the 'Arabian Nights,' which had but to be 

 rubbed and forthwith genii appeared ready to furnish on the 

 spot a palace, a banquet, or anything else that might be required. 

 By persistent application it would appear that insects have 

 been able to evoke from young parenchymatous cells either 

 galls, floral structures, or domatia, as occasion demanded. A 

 strong objection to Henslow's theory is presented, however, by 

 the circumstance that whereas in the case of a gall the feeding 

 of the larvae furnishes a continuous stimulus, in the case of 

 insects visiting flowers the stimulus is interrupted, and only 

 applied occasionally. Although flower -buds are variously 

 modified by gall - makers, Henslow's theory encounters the 

 seemingly insuperable difficulty that no changes of this de- 

 scription induced on plants by insects are known to be ever 

 directly transmitted to their descendants. All Lamarckian 

 theories are, however, open to the same objection. The cir- 

 cumstances under which acquired characters are transmitted 

 are not understood, and until we can give a better account of 



1 B. A. Reports, 1901. 



2 ' Jour. R. Micro. Soc.,' 1888, p. 87. 



