198 STUDIES IN THE POLLINATION ON INDIAN CROPS 



seed boxes in lines at a definite distance between the plants. Provided all due 

 care is taken and the cultures are kept under close observation, especially at 

 the beginning, the danger of contamination through self-sown seed can be 

 avoided altogether. 



II. Some leguminous crops. 

 1. San-hemp.^ 



San-hemp {Crotalaria juncea L.) is widely cultivated all over India mainly 

 for its fibre and as a green manure crop. 



Flowering. The large conspicuous yellow flowers are borne on long ter- 

 minal racemes, the first blossoms appearing when the plants have attained 

 their full height (Plate I). The lowest flower of each inflorescence opens first 

 and flowering proceeds regularly towards the growing point and is completed 

 in the whole plant in about a month. The carina is very pointed, slightly 

 twisted at the apex and closely shut. The stamens are diadelphous and 

 unequal. The anthers of the shorter stamens are linear, of the longer ovate. 

 Those buds which show slits in their calyces in the late afternoon with the 

 yellow corolla showing through, open the following morning about 9 to 10 a.m. 

 at which period the glands begin to secrete nectar freely. As a rule the flowers 

 remain fully open for two days, partially closing at nightfall. Comparatively 

 few of the flowers set seed under Pusa conditions. 



Pollination. In the bud stage (Plate I) the two sets of anthers are in 

 position at a considerable distance below the stigma. When slits appear 

 in the calyx, dehiscence of the linear anthers begins and the filaments of the 

 ovate set of anthers begin to increase in length and to press the liberated pollen 

 towards the orifice of the carina. When the flower is fully open, the stigma 

 (which is provided with a bunch of hairs round the stigma tic surface) lies 

 towards the orifice of the keel and is free from the mass of pollen supported by 

 the ovate anthers which have not yet burst. In addition to the bunch of 

 hairs there is a line of hairs pointing upwards along the whole length of the 

 style. These help to keep the pollen in position. When heavy insects like 

 Megachile anthracina or Xylocopa amethystina alight on the wings and search 

 for nectar, the piston mechanism is set in motion and first the stigma and then 

 a pasty vermiculous mass of pollen are extruded and forced somewhat violently 

 against the hairy abdomen of the insect. The flowers are also visited by 

 Megachile lanata but this insect is too short for the stigma to strike its abdomen. 

 It is however heavy enough to set the piston mechanism in motion and collects 



1 Mem. Dept. of Agr. in India {Botanical Series), III, 1910, p. 177 ; Die ZiicUung derUandw 

 Kulturpflanzen Bd. V, 1912, s. 145. 



