NEWLY-DISCOVERED HABIT IN THE BLACKCAP WARBLER. 



the openings at the base of the petals. These are much wider than 

 in Hibiscus, and all equally visible to the bee. The axis of the 

 flower of Hibiscus, on the contrary, being horizontal instead of 

 vertical, the bee on entering along the upper surface of the 

 stamens sees only two openings through which light appears, the 

 other three being below the point of vision and partly concealed 

 by the stamens. These two openings are [probed by the bee, 

 and they exactly correspond with the spots on the two upper calyx- 

 segments where alone the nectar is found. 



In this fact, and in the absence of nectar in the pink variety, 

 where, from the overlapping of the petals, no openings exist at the 

 base, and also from the fact that no nectar is found in the lowest 

 flowers on the Hibiscus which are not visited by the bees, we see 

 a striking proof of the correctness of the theory that nectaries are 

 due to the irritation caused by insects. 



On this subject Professor Henslow says : — " The glands are 



occasionally borne on the sepals, as of the Lime Hence no 



rule can be established as to the places where one would be likely 



to find honey on a priori grounds With regard to the origin 



of honey-bearing organs or ' nectaries,' there are many reasons 

 for inferring their existence to be due to the direct irritating 

 action of insects themselves when searching for juices as food or 

 otherwise." * 



A device, similar to those above mentioned, I found practised 

 in the Grand Canary on another species of plant, Aloe vulgaris 

 or vera. In this instance the corolla was bitten on the upper 

 surface, close to the base, thus enabling insects to arrive at the 

 nectar easily, which, in consequence of the length and narrowness 

 of the tube, they could not otherwise do. All the flowers of this 

 plant growing near the Gran Caldero were thus mutilated. 



Sitting down to watch, I found that the Blackcap and the 

 smaller Warbler (Phylloscopus fortunatus) visited all the flowers in 

 search of insects. Being somewhat late in the day, I did not see 

 either of them tear the flowers, but this, as a rule, is done in the 

 early morning. The Phylloscopus, indeed, so far as I could 

 observe, did not in any case tear the flowers, but only made use 

 of them when torn by the two other species. 



It is, of course, possible that the Blackcap may, in the first 



* ' The Making of Flowers,' pp. 107, 108, 



