II CRUCIFER^ 87 



are first yellow, then reddish purple, and finally black. 

 As insect visitors 17 species of bees, 9 flies, 2 butter- 

 flies, 2 saw-flies, 1 wasp, and 1 beetle are recorded. The 

 seeds are smooth. The plant grows in mountain dis- 

 tricts in Great Britain. 



T. arvense. — Nectar is secreted by small green glands 

 on each side of the base of the shorter stamens. The 

 anthers of the four longer stamens open inwards at the 

 same time as, and on the same level with, the stigma, 

 so that in the absence of insect visits self-fertilisation is 

 almost certain to occur. According to Kerner the 

 flower is slightly protogynous. The seeds are covered 

 with concentric striae. 



T. perfoliatum. — The arrangement of the flower 

 agrees with that of the preceding species. The seeds are 

 smooth. The plant is recorded in Great Britain only 

 from limestone in Oxford and Gloucester. 



Teesdalia 



T. nudicaulis. — This is one of the species in which 

 the seeds produce a mucous secretion by means of which 

 they adhere to passing animals, and are thus carried 

 about. Possibly also the mucus may tend to fasten 

 them to damp ground, and also prevent them from 

 being eaten. 



Capsella 



0. Bursa -pastoris (Shepherd's Purse). — The name 

 Capsella was given to this genus from the resemblance 

 of the pod to a small purse. The species is said to be 

 called " shepherd's purse" because there is no money in 

 it. The radical leaves form a rosette on the ground, and 

 are very variable in shape, being sometimes entire, 

 sometimes pinnatifid, with a larger ovate, or triangular 

 terminal lobe ; sometimes glabrous, sometimes pubescent. 

 The four nectaries are situated at the two sides of the short 

 stamens. The longer stamens are about as long as the 

 pistil, so that the plant can easily fertilise itself Willis 

 found gynomonoecious and gynodicecious plants, con- 



