22 



PRACTICAL COURSE IN BOTANY 



Experiment 20. The use of adhesive fruits. — Scatter broadcast 

 a handful of hooked or prickly seeds or fruits — cocklebur, tickseed, beggar- 

 ticks, bur grass, etc. Are they suited for wind transportation ? Drop one 

 of them on your sleeve, or on the coat of a fellow student ; will it stay 

 there? What would be the effect if it became attached to the fur of a 

 roaming animal ? Is this a successful mode of dissemination ? 



30 



Figs. 30-32. — 30, A pod of wild vetch, with mature valves twisting spirally to 

 discharge the seed ; 31, pod of crane's-bill discharging its seed ; 32, capsules of witch- 

 hazel exploding. 



ig. Agencies of dispersal. — The means at nature's dis- 

 posal for this purpose, as show^n by the experiments just made, 

 are four ; namely, wind, water, the explosion of capsules due 

 to the withdrawal of water, and the agency of animals, in- 

 cluding man. The first three are purely mechanical. The 



34 35 



Figs. 33-3G. ^ — Fruits adapted to wind dispersal : 33, winged pod of pennycress ; 

 34, spikclet of broom sedge ; 35, akene of Canada thistle ; 36, head of rolling spin- 

 ifex grass. 



last, animal agency, is either voluntary or involuntary, ac- 

 cording as it is conscious and intentional, or accidental merely. 

 Man, of course, is the only consciously voluntary agent. Of 



