1346 A TEXTBOOK OF THEORETICAL BOTANY 



appearing to offer a reward to the visitor though in reaHty the insect may 

 obtain nothing in return for acting as a polhnator. Clearly it is only possible 

 to determine whether a reward is actually given by a careful study of the 

 flower and it is not surprising, therefore, that the well-known cases of this 

 type of mechanism are ones in which the flower is peculiar in construction 

 and has attracted careful study. The methods whereby insects are deluded 

 may differ considerably and there is no general plan common to all. 



(a) Deceptive nectar flowers. One of the most striking examples is Par- 

 nassiapahistris, the Grass of Parnassus (Fig. 1255). It favours the acidic soils 

 and is common in some parts of Britain. The flowers are produced singly and 

 consist of a five-parted calyx and five large, whitish petals. Within the open 

 cup formed by the petals are five fertile stamens which alternate with the 

 petals, while opposite each petal, possibly representing an inner whorl of 

 stamens, are five petaloid scales. Each scale consist of a basal portion, which 

 terminates in a number of slender branches, arranged like the fingers of a hand, 

 each ending in a bright yellow swelling. These swellings glisten and appear to 

 be nectariferous glands, but they are perfectly dry and secrete nothing at all. 

 In the centre is a superior ovary with a sessile stigma. When the flower 

 opens the anthers are still unripe but their filaments soon elongate, one after 

 another, so as to bring each anther in turn over the top of the immature 

 stigma. After the pollen has been shed the anther bends outwards and is 

 replaced by another. About five days later, when the last anther has moved 

 away, the stigma unfolds and is placed in the position previously occupied 

 by the anthers. 



Only a small quantity of nectar is secreted at the base of the corolla, and 

 is generally missed by less intelligent flies who concentrate their attention 

 on licking the yellow pseudo-nectaries. Larger and more intelligent insects 

 settle on top of the flower and turn round and round as they probe between 

 the petals for the nectar. Hence in the early stage they will receive pollen 

 on the lower part of their bodies, while this will be dusted off on the stigma 

 of older flowers. 



{b) Deceptive nauseous flowers. Another and quite different type of 

 deception is found in the flowers oi Paris quadrifolia, a member of the Liliaceae 

 which is found in calcareous British woodlands (Fig. 1256). The offensive 

 odour given out by these flowers suggests that they should belong to the 

 Nauseous Flower group. 



The flowers are yellowish-green in colour and consist of four lanceolate 

 sepals, each about an inch long, inside which are four very narrow petals 

 which often have a yellowish tint. Both the calyx and the corolla segments 

 bend backwards over the stalk, while the eight stamens diverge upwards 

 around the ovary. Each stamen consists of a fine green filament and an 

 almost linear anther, the connectives being prolonged beyond the anther 

 in a long fine process. The anthers open introrsely. The ovary is large and 

 globose, purple in colour and somewhat shiny in its early stage. It is sur- 

 mounted by a style with four or five divergent stigmas. 



The flowers are protogynous and the stigmas are ripe as soon as the 



