1G2 



LETTER XII. 



when they close, like the paper purses that are made 

 for children. These corollas open and close under 

 the influence of light or darkness, some opening 

 only in the day, others only in the night, and in one 

 case (Ipomoea sensitiva) they are so sensitive, that 

 they contract beneath the touch like the leaves of 

 the Mimosa. The calyx of the Bindweed consists of 

 five sepals, which overlie each other so sompletely, 

 that you can seldom perceive more than the two 

 outermost. The fruit {fig. 5.) contains three or four 

 cells, and a very small number of seeds, the embryo 

 of which ( fig. 7-) is doubled up in the most curious 

 way, just as if there were not room enough within 

 the seed for it to grow. The roots of many of them 

 are large and fleshy ; they possess powerful medicinal 

 properties, and are fit for food only in the case of the 

 Sweet Potatoe (Convolvulus Batatas), which was so 

 much esteemed before the common Potatoe displaced 

 it in Europe. 



To this tribe also belongs an odd little plant called 

 Dodder (Cuscuta). Have you never remarked upon 

 the stems of the Heath, or Nettles, or of the Furze, 

 clusters of stout reddish cords which are so twisted 

 and intertwined that you would take them for a knot 

 of young snakes, if the colour first, and then their 

 touch did not undeceive you. If ever you have ob- 

 served so strange an appearance you have seen 

 Dodder, which, originally earth-born, soon lays hold of 

 some neighbouring plant, twists her leafless shoots 

 around it, fixes them firmly to the branches, quits her 

 hold of the soil, and thenceforward, as if ashamed of 



