THE BLACK NIGRITELLA 135 



and then below, in addition to ordinary roots, a 

 pair of tuberous roots, white and fleshy, which 

 are of different ages (Plate XXXL, Fig. 1). Both 

 are storehouses for reserve food material. The 

 larger tuber contains the nourishment for the flower- 

 ing stem, and was in existence last year. The 

 smaller tuber dates from the present year, and in 

 it will be stored reserves during the summer to 

 further the growth of next year's shoot. The same 

 state of affairs will be found in the case of the Lesser 

 Butterfly Orchid. The leaves are rather thick and 

 narrow. They wrap round one another at the base, 

 and are enclosed in one or more scale leaves, of a 

 brownish colour and thin papery texture. At the 

 base the leaves are white and fleshy, no chlorophyll 

 (see p. 10) being developed below ground because 

 light is absent. The flower-stalk springs from among 

 the leaves which invest it at the base. 



We thus see that the Black Nigritella, like most 

 Swiss Orchids, is a pronounced geophyte (see p. 125). 

 Its storehouses of reserve food lie buried deep in the 

 soil, away from the dangers of winter frosts. 



The flowers, like those of many other Orchids, have 

 a strong scent, in this case resembling that of vanilla. 

 Vanilla itself is obtained from the fruits of a tropical 

 climbing Orchid, known botanically as Vanilla plani- 

 folia, Andr. The structure of the flowers of the 

 Orchids, as is well known, is specially adapted to 

 insect visitors, and to cross-fertilisation by their 

 agency. Those of the Black Nigritella are perhaps 



