vii Relations Between Plants and Animals 137 



of constructing so ingenious a habitation. The fleshy sub- 

 stance of this formicarium is formed of cellular tissue ; the 

 channels and galleries with which it is perforated have their 

 entrance near the lower part of the tuber." 



Unluckily for Caruel and Beccari, the development of Myr- 

 mecodia has been reinvestigated lately by Treub, 1 in Java, 

 who sadly diminishes the wonder by showing that the plant 

 can thrive without its guests, and that the galleries are 

 formed and grow as congenital peculiarities without the aid 

 of ants. By rearing plants from the seed, in the absence 

 of all ants, he has been able to study the growth of the 

 tuberosities. They seem to him to be at first reservoirs in 

 which water is stored for the needs of the plant, the firm 

 outer surface (devoid of stomata or lenticels) preventing eva- 

 poration. The ants simply use these when dry as dwellings, 

 without in any marked way benefiting the plant. This is a 

 fresh lesson of caution, and of the risks of Darwinising 

 over-much. A good specimen may be observed at Kew. 



Galls. These interesting domatia above referred to 

 must of course be distinguished from the galls which 

 many insects form on plants. Every one knows the large 

 gall-nuts (rich in tannin and gallic acid, both useful in ink- 

 making, etc.) formed on oak-leaves by wasp-like insects of 

 the genus Cynips, and the strange " Bedeguar " tufts so 

 common as mossy excrescences on wild roses. These 

 abnormal growths are produced by a remarkable vegetative 

 increase of the tissues of the plants. This is due to the 

 irritation produced by the gall-flies, or rather gall-wasps, 

 which lay their eggs in the soft substance of the plant. 

 Here again, as with lichens or ants, or what not, we are 

 but at the threshold of a new subject with its literature and 

 its specialists. For along every main road of the organic 



^'Nouvelles Recherches sur le Myrmecodia de Java," Annalts 

 du Jar din Botanique de Buitenzorg, vol. vii. (1888), p. 191. 



