422 BIOLOGIC RELATIONS BETWEEN PLANTS AND ANTS. 



attacked by the larvae of Hylotoma. Incommoded by the ants, these 

 larvae took refuge upon the youngest buds, unprovided as yet with 

 nectaries, and consequently not visited by ants. It is to be remarked 

 that the Banks rosebushes, which are rarely or never attacked by 

 Hylotomas, are destitute of prickles. We may probably admit that 

 there is a correlation between the presence on plants of thorns or prickles 

 and that of leaf-eating insects. Is it not due to the protection given 

 by ants and other sting-bearing hymenoptera that the Banks rosebushes 

 attain the great age that some of them are known to do ? We may cite 

 as an instance one of these bushes planted in 1803 by Bopland in the 

 garden of the marine hospital at Tonlon, which has a stem a meter in 

 diameter at the base and bears each year from fifty to sixty thousand 

 flowers. 



The leaves of peach, apricot, and cherry trees may, as there is reason 

 to suppose, be derived from compound leaves. The nectaries which 

 they carry on the petioles should then have the significance of aborted 

 leaflets filled with sweet stores. 



The extranuptial nectaries belong not only to phanerogams, they 

 are also found in the vascular cryptogams. We find extranuptial 

 nectaries at the base of sterile pinnules in Pteris aquilina and Acrosti- 

 chum scandens. In Acrosticlium Horsfieldii we find at the base of the 

 sterile leaflets, and also frequently at the base of the fertile leaflets, 

 small auricles that seem to be nectariferous. 



Francis Darwin, who discovered the nectaries in the fronds of Pteris 

 aquilina, does not believe in the defense afforded by the ants against 

 phytophagous insects. In favor of this theory, however, is the fact 

 that the secretion of nectar takes place only in young fronds whose 

 tissue, yet tender, is an easy prey for the leaf eaters. It should also be 

 noted that Pteris aquilina is a cosmopolitan plant. It may not attract 

 insects in England, and yet do so in other regions. Besides, in France, 

 an Halictus has been seen to visit the fronds of this fern. Ferns are 

 not exempt from attacks by plant-eating insects. Beccari saw a 

 Cyrtomium pUcatum, cultivated in a court, with all its fronds covered 

 by a green caterpillar. Not far from this fern were found stems of 

 Pteris aquilina which had been reduced to small fragments by an 

 insect. Beccari supposes that the same larva attacked simultaneously 

 the fronds of the two ferns. 



It is not only the normal organs of plants which may offer a sugary 

 secretion prized by the ants. Certain galls may be considered as true 

 foliary nectaries of parasitic origin. "The galls of Andricus testaceipes 

 (Aphilotrix Sieboldi)," says Adler, "are greatly exposed to the attacks 

 of various parasites of the genera Torymus and Synergus. It is inter- 

 esting to observe how the gall has indirectly evolved a means of pro- 

 tection. Its red, sappy envelope secretes a sticky fluid eagerly sought 

 after by ants, and that they may enjoy this nectar undisturbed, they 

 build with sand and earth a perfect dome over the galls, and in this 



