THE WEEDS OF NEW SOUTH WALES. 



5. " Boring " or Hygrometric seeds which irritate animals. 



In certain species of Stipa (Spear Grass), the awn is very sensitive to even 

 slight changes in the moisture of the atmosphere. If it should happen to fall 

 on a sheep's back the free end of the awn catches on the wool, and as it 

 twists and untwists, must force the sharp point at the base of the glume 

 into the skin (the rigid hairs pointing upwards, prevent its ever being with- 

 drawn), so that every change of the twisting awn forces the sharp point 

 down into the skin, and sheep are killed in this way. See the Agricultural 

 Gazette for 1894, p. 135. 



The ordinary function of these twisting awns is, of course, to bury the 

 seed in the ground. 



See also an article by Mr. J. D. Stewart in the Agricultural Gazette for 

 1901, p. 357, on the "Injurious Effects of Certain Grass Seeds to Live 



Stock." 



S. spartea, the " Porcupine Grass " of the United States, bears the same 

 reputation in that country that S. setacea does with us. See Pammel, 

 p. 355. 



Heteropogon contortus, the " Bunch Spear Grass " (see the Agricultural 

 Gazette for 1892, p. 856), is even more formidable than Stipa, but fortu- 

 nately it is less widely distributed. Some species of Aristida, the '' Three- 

 pronged Spear Grass," may also injure sheep in certain seasons. 



Andropogon acicularis Retz. Mr. Henry O. Forbes has an interesting 

 note in Nature xx, p. 456, on the irritation produced by seeds of Andtopogon 

 acicularis Retz. on his own skin when he was in Java. 



Triodia. Warburton (Warburton's Explorations, by C. H. Eden, p. 156), 

 in referring to the so-called " Spinifex," or " Porcupine Grass " of Western 

 Australia (Triodia), says that to horses it has on more than one occasion 

 proved most destructive, piercing and cutting their legs, which in a very 

 short time become fly-blown, so that the animals have either to be destroyed 

 or abandoned. 



SECTION 2. DISPERSAL OF WEEDS BY NATURAL MEANS. 



Weeds Distributed by the Wind. 



1. Seeds dust-like. 



2. Weeds with silky hairs. 



3. Weeds with wing-structure 



4. Weeds with " tumble-weed " structure. 



1. Weeds with seeds fine as dust. 



Among such seeds is the Poppy (Papaver hybridum), but there are very 

 many kinds. They may be caught up by a breeze and deposited miles away 

 from the parent plants. Obviously it is difficult to control an invasion of 

 plants which behave like this. 



In Proc. Linn Soc. N.S.W., 1901, p. 697, Mr. R. H. Cambage points out 

 that whirlwinds out west are responsible for the distribution of seeds even 

 of large size. 



