126 ARISTOLOCHIA GIGAS 



virtues of the nettle family, we are bound 

 to conclude that the latter outweigh the 

 former, and that nettles are most useful 

 plants, even if troublesome when touched in- 

 cautiously. There are one or two facts about 

 the nettle which we must not omit to notice. 

 The ease with which the sting penetrates the 

 human skin is accounted for by the fact that 

 its walls are composed of flint, as may be 

 easily proved by heating it red-hot on a plate 

 of mica. If the sting be carefully removed 

 from the growing plant, the streaming of the 

 protoplasm can be distinctly seen. The cuticle 

 shows oblique striation, which ascends in the 

 same direction in all stings. 



As already stated, the illustration (Fig. 36) 

 is from a photo-micrograph, showing the sting 

 as if enlarged to 100 diameters ; the focal dis- 

 tance was 45 inches, and a half-inch objective 

 was used. 



Aristolochia gigas. 



A section of this remarkable plant is shown 

 in the illustration. Its peculiarity is at once 



