Ch. VII, 3] DISSEMINATION OF PLANTS 



359 



•^7?, 



(Cotton), ovary (Willow), calyx (Composite), 'persistent style 

 (Clematis), and aborted flower stalks (Smoke Bush). Here 

 also, it is likely, the general principle of modification along 

 lines of least resistance explains the 

 particular cases. 



Another mode of wind dissemina- 

 tion is found in the "tumbleweeds." 

 In these the flower cluster, as in some 

 members of the Parsley Family, or 

 else the entire plant, as in Russian 

 Thistle, becomes detached, incurls 

 the branches, and thus is rolled over 

 open ground, scattering the seeds as 

 it travels. Such plants are espe- 



Fig. 254. — Seed of Cot- 



cially characteristic of open plains ton ' , wl ^ h the important 



r™ -d - j . £ c long hairs; X }. (From 



country. The Rose of Jericho, ot Figurier.) 

 the Scriptures (Fig. 257), is said to 



have this habit, thus giving a concrete meaning to the scrip- 

 tural phrase "blown like stubble before the wind." 



It is also the wind which scatters, though indirectly, the 

 small, rounded, smooth seeds formed in so many kinds of pods 

 upon long stalks, such as the Poppy (Fig. 239) ; for such seeds 



seem to be shaken forcibly 

 from the pods when struck by 

 strong gusts in autumn and 

 winter. It has been claimed 

 that the pods have such form 

 and angles of exit as to guide 

 the seeds well away from the 

 plant. 



Finally (in so far as we can 

 take space to discuss this phase 

 of our subject), the wind effects 

 dissemination of very minute spores or seeds without any 

 special arrangements. The method rests on the fact that 

 as a body decreases in size, its bulk diminishes far faster 



Fig. 255. 



Seed of Milkweed 

 X I 



