CHAP. .. SECRETION OF NECTAR. 405 



bracteae, or flower peduncles, or on the outside of their 

 calyx, and these glands secrete minute drops of a sweet 

 fluid, which is eagerly sought by sugar-loving insects, 

 such as ants, hive-bees, and wasps. In the case of 

 the glands on the stipules of Vicia sativa, the excre- 

 tion manifestly depends on changes in the sap, con- 

 sequent on the sun shining brightly ; for I repeatedly 

 observed that as soon as the sun was hidden behind 

 clouds the secretion ceased, and the hive-bees left the 

 field ; but as soon- as the sun broke out again, they 

 returned to their feast.* I have observed an analogous 

 fact with the secretion of true nectar in the flowers of 

 Lobelia erinus. 



Delpino, however, maintains that the power of 

 secreting a sweet fluid by any extra-floral organ has 

 been in every case specially gained, for the sake of 

 attracting ants and wasps as defenders of the plant 

 against their enemies ; but I have never seen any 

 reason to believe that this is so with the three species 

 observed by me, namely, Prunus laurocerasus, Vicia 

 sativa, and V. faba. No plant is so little attacked by 

 enemies of any kind in this country as the common 

 bracken-fern (Pteris aquilina) ; and yet, as my son 



on the leaves in the bud bear (harz). 



glands which secrete only at a * I published a brief notice of 



very early age, and which have this case in the ' Gard. Chronicle.' 



the same morphological structure 1855, July 21, p. 487, and after- 



as true nectar-secreting glands. wards made further observations. 



He further shows that the nectar- Besides the hive-bee, another 



secreting glands on the petioles species of bee, a moth, ants, and 



of Prunus avium are not deve- two kinds of flies sucked the 



loped at a very early age, yet drops of fluid on the stipules, 



wither away on the old leaves. The larger drops tasted sweet. 



They are homologous with those The hive-bees never even looked 



on the serrations of the blades of at the flowers which were open 



the same leaves, as shown by at the same time; whilst two 



their structure and by transition- species of humble-bees neglected 



forms ; for the lowest serrations the stipules and visited only the 



on the blades of most of the leaves flowers, 

 secrete nectar instead of resin 



