228 RECEPTION OF FLOWER-SEEKING ANIMALS AT THE FLOWER. 



former has two hollow projecting pegs which give the whole flower a homed 

 appearance (fig. 257^), that of the latter two pegs, also hollow (fig. 257^). In 

 the Snapdragon (Antirrhimcm) and in the allied Toad-flax (Linaria) two remark- 

 able knobs, projecting from the lower lip, serve as a platform for insects which, by 

 exerting pressure, force down the lower lip and gain access to the flower. It is 

 most entertaining to observe how a Humble-bee buzzes about till it alights on the 

 two knobs of the lower lip, and then, having opened the mouth by means of hinges 

 on either side of the corolla, suddenly disappears into the cavity of the flower to 

 fetch honey. In the Calceolarias the phenomenon is even more remarkable. The 

 Humble-bee sits on the inflated, slipper-like lower lip, and opens the mouth by 

 a light pressure against the upper lip. Then a nectary, hitherto hidden in the 

 slipper-like cavity, comes to light, flap-like, and amply provided with honey. This 

 nectary is presented to the Humble-bee just like a spoon as it sits on the lower lip. 

 Directly the bee goes the lower lip snaps to, and the nectary disappears from view. 



An interesting mechanism obtains in the flower of Corydalis lutea {cf. figs. 

 257 ^ and 257 ■*). The corolla here consists of four petals, one right and one left, 

 one above and one below. The two latter are similar and applied together like 

 two hollow hands. The right-hand petal is small and spoon-shaped, the left-hand 

 one is the largest of all, and is produced outwards into a short spur which contains 

 honey, whilst above it expands into a sort of brim. Access to the honey is 

 obtained beneath this brim, and insects must enter here. To accomplish this the 

 insect sits on the two median petals, which are applied together (fig. 257 ^). But to 

 give it a better hold, each of these petals has a median flap, which may be compared 

 to stirrups on either side of a saddle. On these the bee gets a purchase, sitting as 

 it were on a saddle. It may be noted here incidentally that the pollen is scattered 

 on the under surface of the abdomen of the insect by a curious lever-mechanism; 

 also that Corydalis is almost unique amongst flowers in that it is lob-sided, i.e. 

 the spurred petal is not in the median plane of the flower (as in the generality of 

 zygomorphic flowers) but is inserted laterally. 



Many Papilionaceous flowers have a considerable resemblance to Corydalis, 

 although their flowers are constructed on quite a difierent plan. The Papilionaceous 

 flower has five petals. Of these the two front ones are united together and form 

 the " keel ", the two lateral are known as the " wings ", whilst the posterior unpaired 

 one is expanded and is known as the "standard". This standard closes the 

 entrance to the base of the flower, where the honey is concealed, from behind so 

 that insects seeking honey must sit either on the keel or wings. In the flowers 

 of Sainfoin (Onobrychis) the wings are quite small and invisible, and here the 

 relatively big keel serves as alighting -platform. In many others, on the other 

 hand, e.g. in Coronia, Orobus, Lotus, and Spartium, the wings are folded over the 

 keel, and meeting in the middle form a sort of cushion well suited as the alighting- 

 place of insects. 



All the flowers so far described have the peculiarity that their petals are 

 not symmetrically arranged all round. Their right and left halves agree abso- 



