68 



THE BOOK OF NATURE STUDY 



pale blue flowers, but these are less common, although they too 



belong to limestone. 



An interesting plant, on account of the 

 arrangement of its leaves, often found on 

 oolitic limestone, is the Yellowwort. The 

 two leaves join at the base to form a ring 

 round the stem, which thus appears to pass 

 through them. They are greenish grey in 

 colour, and the flowers a bright yellow. The 

 blossoms are closed when the sun is not shin- 

 ing, and they remain on the plant long after 

 they have faded, in fact, until the seed 

 vessel splits them up. 



Certain Orchids belong to pastures, and 

 very often to a limited area of the pasture. 

 This seems to be a characteristic of Orchids 

 as a rule ; they are often abundant, but local. 

 The Spotted Orchis (0. maculata) is common 

 in early spring ; in summer the Frog Orchis 

 (Habenaria viridis) and the fragrant Haben- 

 aria are found in hilly limestone pastures. 

 The flower of an Orchid differs in many re- 

 spects from other flowers. It has one stamen 

 which is united with the ovary ; this latter 

 structure is usually twisted, and appears to 



be at first sight the stalk of the flower. The 



pollen grains are united together in masses, 



which adhere to the insect's proboscis as 



they are touched. This is easily seen by in- 

 serting a sharp pointed pencil into the spur of 



the corolla. In this way cross-pollination takes 



place. The Frog; Orchis has brownish green 



u j i_ -L.J- - i- !_ i_ AU FlG - 29. Flower of 



flowers, and grows about eight inches high; the anOrchid< />Lower 



FlG. 28. Yellowwort 

 ( Chlora perfoliata). 



petal ; /, petals ; s, 

 sepals ; //, pollen 

 bags. 



lip petal (labellum) is three -lobed and hangs 

 straight down ; the other leaves of the perianth 

 arch over like a hood. The Fragrant Haben- 

 aria is bigger, and may be even two feet in height. The purple 

 flowers are borne on a long spike, and the spur of the lip is 



