THE WEEDS OF NEW SOUTH WALES. 11 



An analogous contraction of the fruit capsules is responsible for the jerk- 

 ing out of the seed in a number of plants. 



Such an arrangement is useful to the plant in that, it extends the area 

 over which the seed may be sown. 



General. 



The chapter on " The Dispersion of Species by means of Fruits and Seeds/' 

 in Iverner and Oliver's " Natural History of Plants," ii, 833, is well worthy 

 of perusal, if only for its beautiful and helpful illustrations. 



The authors separately figure what they call sling fruits (those in which 

 the seeds are expelled by torsion) ; creeping or hopping fruits (in which the 

 mechanism is hygroscopic bristles) ; fruits which open upon being wetted 

 \vith water; and an especially fine series to illustrate the dispersion of fruits 

 and seeds by the wind. The same work also illustrates sticky fruits and 

 fruits furnished with hooks, &c., to facilitate dispersal by animals. 



Another useful paper for reference is " Migration of Weeds," by Lyster 

 H. Dewey, in Year-book of Agric., U.S.A., 1896, p. 263. The illustrations 

 of seeds carried by winds, &c., are useful. 



SECTION 3. DISPERSAL OF WEEDS BY ANIMALS, 



1. Mechanically by adherence to their coats and feet. 



(a) Fruits with burrs. 

 (6) Adhesive fruits. 



(c) Gumminess of some seeds. 



(d) Weeds transported by the feet. 



2. Transport by wool-washing. 



3. Weeds and manure. 



1. Dispersal by adherence to coats and feet, 

 (a) Fruits with burrs. 



Some of the Medics (Medicago) have twisted pods with marginal hooks 

 forming burrs. Most of the Medics make excellent forage, especially for 

 sheep, and the plants often die down, leaving an enormous quantity of these 

 burrs, which are licked up by sheep and are very nutritious. At the same 

 time, they find their way into the fleece and do a good deal of damage. Up- 

 to-date pastoralists are doing all they can to encourage the spread of those 

 Medics which have pods without burrs. Some of these (M. orbicularis and 

 M . scutellata} are figured in the Agricultural Gazette for 1894, p. 5. 



The largest Medic burr is that of M. intertexta L., which is described in 

 the Agricultural Gazette for February, 1904. 



Amongst grasses we have Cenchrus australis, the burry fruits of which 

 Mr. A. M. Lea has illustrated in Trans. Roy. Soc. S.A., xxxix, 92, under the 

 name of " An insect-catching grass." It mats the hair of any animal which 

 touches it. Lappago (Trayus) racemosus is another burr grass, figured in 

 the Agricultural, Gazette for 1896, p. 129. 



Other plants with burrs are the "Native Carrot" (Daucus brack iatus), 

 and the Acoena, of which we have two species, sanguisorb(K and ovina. 



Then everyone knows the Bathurst Burr (Xantliium spinosum), and its 

 close relation, the Noogoora 'Burr (X. strumarium) figured in the Agri- 

 cultural Gazette for July, 1917, p. 489, and October, 1899, respectively. 

 These are typical burrs. 



