46 THE AMERICAN BOTANIST. 



other which is half immersed. Now, some species of 

 "teasel" have the opposite leaves so united around the 

 main stem as to form a cup. This is partly filled with 

 water, which, of course, isolates all the stem above. 



In our \vater knot-weed, a plant common to iDoth 

 hemispheres, if the individuals are growing in water, no 

 hairs are developed on the stem. If, however, it happens 

 during the summer that the pond dries so far as to strand 

 the plants, at once protective hairs make their appear- 

 ance. Great use is made of hairs by man}' plants. Often 

 the}' have their points directed in the way of intruders, 

 much like a military chevaux-de-frise. Insects readily pass 

 over them -when proceeding, so to speak, ivit/z the grain, 

 but are much embarrassed by them when going in the op- 

 posite direction. Wool or down, too, is often an effective 

 hindrance to ants, aphides, etc. Slugs are excluded by 

 sharp prickles. As in the case of law, total prevention is 

 not expected, but a reduction of crime to a minimum. If 

 all the contrivances succeeded we should have the millen- 

 ium. 



The fearful little spines of the prickh'-pear, or bayonet 

 like thorns of other Cactacje, make them formidable to the 

 largest animal. Nemo me impune lacessit is the motto of 

 the thistle, poetically' assumed by Scotland. "Touch-me- 

 not" is the fighting word oi Jatropha urens and many a 

 stinging nettle. "Don't tread on me," the warning of bur- 

 grass. Look at the prickles of nettle under a glass and 

 see Avhat a fang is here — a serpent-tooth with a poison 

 gland ! 



Prickles, as in the rattan, and some other plants, often 

 serve another purjoose ; the}- aid the plant in climbing. 

 The rattan, according to Wallace, has been found 600 or 

 even 1,000 feet in length. It attaches itself to the jungles 

 and copses by its prehensile hooks. 



Acrid, poisonous or sticky secretions are much used b}- 

 plants in their defence. The reader will at once think of 

 many plants provided with such juices — the milk-weeds, 

 spurges, dandelions, celandines, lettuces, hawkweed, pop- 



