22G A BOOK OF INSECTS 



album). Here the five petals are united to form a tubular 

 corolla, with a broad lip which serves as an alighting place 

 for insects, and a hood which protects the essential organs. 

 There are only four stamens, the anthers of which lie 

 beneath the hood. The style of the pistil rises between 

 the filaments of the stamens, and ends in a two-lobed 

 stigma. Nectar accumulates in the narrow, basal part of 

 the corolla, and is protected from unbidden guests by a 

 ring of hairs. Humble-bees are the chief visitors. They 

 alight on the lip, and thrust their heads into the neck of 

 the corolla to reach the nectar. In so doing the bee first 

 touches the stigma, which is thus likely to receive pollen 

 brought from another flower, possibly from another plant. 

 A further supply of pollen is deposited by the anthers on 

 the insect's back, and this will be carried to the next 

 flower visited. Since the stigma is receptive when the 

 anthers are shedding their pollen, the flower may readily 

 be self-pollinated through the agency of insects ; but be- 

 cause the flowers are frequently visited, and the bees 

 pass rapidly from one to the other, the chance of cross- 

 pollination is very great. A somewhat similar adjustment 

 is seen in the yellow iris, or flag (Iris pseudacorus). The 

 three outer leaves of the perianth are large, spreading, and 

 recurved, the three inner ones small and erect. All six 

 join together at their bases to form a short tubular region 

 wherein nectar is secreted. This accumulates round the 

 bases of the styles, and is reached by the insect through 

 minute channels on either side of the stamens. The three 

 styles are petal-like, and arch over the corresponding 

 stamens and outer segments of the perianth, the stigma 

 being a projecting lip on the under surface of the style. 

 Each third of the iris bloom may therefore be likened 

 to an irregular flower. Pollination is mainly effected by 

 humble-bees. In order to reach the nectar, the insect 



