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In order to prove that the secretion of sugar by attracting harmful 

 insects is indeed injurious to these trees it would still be necessary 

 to show that they remain uninjured when the secretion of sugar 

 does not take place. This proof is readily afforded by some other 

 Malvaceae. 



Two shrublike Malvaceae of common occurrence in India, namely 

 Hibiscus rosa sinensis L. and Hibiscus tiliaceus L. have nectaries 

 on their leaves. They are not frequented by ants or other harmful 

 insects, however, because in the nectaries, as far as my observations 

 go, a fungus always occurs, which may be recognised already from 

 the outside b}^ its black Colour. This fungus prevents the secretion 

 of sugar, and the nectaries cease to have an attraction for insects 

 which otherwise would be harmful to the plant. These shrubs by 

 their healthy appearance contrast strongly with the above mentioned 

 plants in the Malvaceae quarter, which are frequented by ants and 

 other insects. 



On account of the circumstance that the extrafloral nectaries are 

 found chiefly on and near the inflorescences, Burck proposed the 

 hypothesis, that in some cases they would serve to attract ants into 

 the neighbourhood of the flowers in order to protect these against 

 bees and wasps, which would bore them and rob honey. But even 

 with the plants investigated by him I could find no confirmation of 

 his hypothesis. First the nectaries only rarely occur on the inflores- 

 cences exclusively; also the plants mentioned by him as proof as : 

 Thunbergia grandijiora Roxb., Gmelina asiatica L., and Gmelina 

 bracteata, Nycticalos macrosj/phon and Nycticalos Thomsonii cannot 

 serve as examples, since these plants also on their vegetative parts 

 such as leaves and stems possess nectaries, which according to him 

 are not present there or are not mentioned. In regard to the so-called 

 "food-bodies" (BuRCK'sche Körperchen) on the calyx of Thunbergia 

 grandijiora, it appeared to me that these are no "food-bodies" at 

 all, but ordinary sugar-secreting deformed hairs which I also found 

 on the bracts, leaves and leaf-stalks of this plant. 



Further it appeared to me that the number of bored flowers stands 

 in no relation to the number of nectaries occurring on the calyx, 

 as should be the case according to Burck. It is much more dependent 

 on external factors, as e. g. the more or less free situation of the 

 plants, the weather etc. 



As an example the creeper Bignonia Cliamberlaynii may be men- 

 tioned. Of this plant on many days only 1,6 "/o of the fallen flowers 

 appeared not to have been bored by Xylocopa coeridea, although 

 numerous ants always occur on the nectaries of the calyx. 



