192 VEGETABLE SUBSTANCES. 



that the cow-thistle did appear very bitter to them 

 when they first learned to eat it. As soon as it be- 

 gins to bloom, the stalk becomes woody, and is no 

 longer edible. 



The WATER-CRESS. Nastvrtwm officinale 

 which was probably used freely by our simple an- 

 cestors, is still a luxury of the crowded city. In 

 most parts of the country it is still found abundantly 

 in a state of nature, growing in ditches and brooks, 

 preferring clear water, and especially the water of 

 springs, to that which is foul and stagnant. For an 

 obvious reason we must somewhat minutely describe 

 the water-cress. 



This plant is a trailing perennial, putting out root- 

 iets at the joints of the stems. The leaves, which 

 have a slight tinge of purple, are pinnate and rather 

 heart-shaped. When the current in which they 

 grow is rapid, the rootlets from the young shoots do 

 not easily take root, and then a considerable portion 

 of the plant rises above the surface of the water and 

 the form of the leaves alters. This is the case with 

 many plants ; when the leaf is near the ground it is 

 broad, but when elevated it becomes longer and 

 narrower. In water-cresses, this change in the 

 form of the leaves is sometimes followed by un- 

 pleasant consequences, since it then causes them to 

 be similar in shape with the joint-flowering water- 

 parsnip (slum nodiflorum) , a plant which very 

 generally grows mixed with the cresses, and has 

 poisonous qualities. The leaves of the cress are 

 however more smooth and shining, and are entire at 

 their edges, while those of the parsnip are serrated. 

 When the flowering stems are up, the plants are 

 easily distinguished. The water-parsnip bears its 

 flowers in umbels close upon the joints of the stem, 

 while the flowers of the cress are cruciform and rise 

 into a spike. The four petals in the flower of the 



