CRUCIFER.. 159 



have seen the instrument called a hygrometer, which is con- 

 structed to measure the degree of moisture in the atmosphere. 

 But to return to our subject, this hygroscopic nature is not, it 

 appears, peculiar to the Rose of Jericho, but is also possessed 

 by other plants; and the same quality has been lately dis- 

 covered in the capsule of the CEnothera, or Evening Primrose. 

 Many ridiculous stories have been circulated respecting the 

 Rose of Jericho, but they are all destitute of foundation, 

 except in the curious property which I have just related.* 



MARY. 

 Is the plant annual 1 ? 



ESTHER. 



Yes. It bears small white flowers, and is one of the 

 family of Oruciferee. 



MRS. F. 



The flowers of almost all this family are either white or 

 yellow. The pretty annual Heliophila is, I believe, the only 

 exotic genus which is blue; and the Braya alpina, and Jlrabis 

 coerulea of the Alps, the only two blue species which are 

 natives of Europe. 



HENRIETTA. 



But do not yellow flowers sometimes have blue varieties? 



MRS. F. 



Never. It is an established fact, with regard to the colors 

 of flowers, that an originally yellow flower may alter to rose, 

 red, or white, but never to blue; and vice versa, a blue flower 

 will never by cultivation, become yellow. f 



HENRIETTA. 



But there is a yellow and a blue irisT 



MRS. F. 

 True: but they are distinct species, and it is of varieties 



* Art. Jerose, in Diet. Sciences Naturelles. 

 t De Candolle on Cruciferw. 



