BIOLOGIC RELATIONS BETWEEN PLANTS AND ANTS. 423 



way provide the inhabitants with the best protection against their 

 enemies. 



There are other honey-dew galls that furnish ants with an excellent 

 food. Such are the reddish-brown galls formed on the leaves of the 

 Quercus undulata in the region of the Garden of the Gods, Colorado. 

 These galls are frequented by the honey ant, Myrmecocystus melligcr, 

 whose habits, studied by McCook, have been recounted in most classi- 

 cal treatises. We need here only recall that these ants have two 

 classes of workers — those charged with gathering nectar from the sur- 

 faces of the galls and sedentary honey-bearing workers whose abdomen 

 is distended by the expansion of a bag filled with honey. The honey 

 bearers do not form a class predestined to special functions by a pecu- 

 liar physical organization. All neuter individuals may be transformed 

 into honey bearers under the influence of special alimentation. There 

 is no doubt but that the presence of ants upon the leaves of the gall- 

 bearing oak may have for its indirect result the protection, first of the 

 galls and then of their leaves, from the attacks of their various enemies. 

 In this case the hymenoptera causing the galls render a service to the 

 plant they attack by attracting to its vegetative organs a more or less 

 permanent army of defenders. 



The Camponotus inflatus and Melophorus Bagoti described by Lub- 

 bock are also honey ants. The Crematogaster inflatus of Malasia has 

 its metathorax transformed into a bag filled with a sugary liquid and 

 provided at the back with two orifices of discharge. 



The production of nectar is not limited, as is well known, to the vege- 

 tative organs of plants. It is especially abundant in the floral organs 

 where the nectaries attract polleniziug insects. The presence of the 

 nectar attracts not only winged insects especially adapted to pollination 

 but also aptera, ants in particular. In a number of cases the latter 

 insects may rob a plant of its nectar without pollination being, in its 

 turn, well assured. Hence we find a series of defensive or myrmecopho- 

 bic arrangements having for their result the exclusion of ants from the 

 floral organs. 



It seems that, to low-growing flowers like certain Cruciferre and Com- 

 posite capable of pollination by ants, there is a certain advantage in 

 the process being effected in a more assured manner by winged insects 

 (Kerner). The chevaux de frise, to which we have called attention as 

 surrounding the inflorescence in the carline thistle and the centaury, 

 may be a defensive organ of the first rank. The wood scabish (Knautia 

 (Upsacifolia) has on its stem downward-pointing hairs through which 

 the ants can not mount to the inflorescence. The teasels are protected 

 by a sort of cup formed by the base of opposite leaves, a cup to which 

 has been ascribed a very doubtful carnivorous function, from which the 

 name "digestive trap," given it by Francis Darwin. 



Vaucher showed some time ago that the Malvaceae that have nectar- 

 iferous flowers are provided with hairs, while those that do not produce 



