44 A HALF-HOUK WITH THE 



the hairs of the common stinging-nettle, represented 

 at figure 88a. 



The hairs constituting the down or " pappus " of 

 compositous plants assume a variety of forms. The 

 Beed or fruit of the common groundsel has a beau- 

 tiful crown, given at figure 245, in plate 8. The 

 pappus of the dandelion appears notched, as seen 

 at figure 246. The burdock has a cottony hair, 

 while the goatsbeard is like a feather, both of 

 which are represented respectively in figures 247 

 and 248. 



If a hair is examined in its growing state, with 

 an object-glass of one quarter of an inch focus, a 

 movement of the particles in its interior is often 

 observed. This is easily seen in the hairs around 

 the stamens of the common Spiderwort (Trades- 

 cantia Virginica). Such movements are very com- 

 mon in the cells of water plants. One of those 

 most commonly cultivated in aquavivaria at the 

 present day, the Valisneria spiralis, affords the best 

 example of this interesting phenomenon. In order 

 to observe this movement, a growing leaf of the 

 valisneria should be taken, and a longitudinal slice 

 should be removed from its surface, by means of a 

 sharp penknife or razor. The slice, or the sliced 

 part leffc on the leaf, should now be put on a slide, 

 a drop or two of water added, and covered with a 

 thin piece of glass, when, after a little time, espe- 

 cially in a warm room, the movement will be ob- 

 served. This movement takes place in the little 

 particles around the sides of the cells represented 

 in figure 886, plate 3. It may also be seen in 

 the leaves of the new water-weed (Anacha/ris 

 alsinastrurri), the frogbit, the rootlets of wheat, in 

 the family of charas, and in the cells of many other 

 water plants. In examining some species of Chcvra, 

 the external bark, or rind, should be removed frora 



