III.] SEED CARRIED BY WIND. 67 



Handbook of the British Flora, the two cells which 

 contain no seed actually become larger than the one 

 which alone might, at first sight, seem to be normally 

 developed. We may be sure from this that they 

 must be of some use, and, from their lightness, they 

 probably enable the wind to carry the seed to a 

 greater distance than would otherwise be the case. 



In other instances the plants themselves, or parts 

 of them, are rolled along the ground by the wind. 

 An example of this is afforded, for instance, by a kind 

 of grass {Spinifex squarrosus), in which the mass of 

 inflorescence, forming a large round head, is thus 

 driven for miles over the dry sands of Australia until 

 it comes to a damp place, when it expands and soon 

 strikes root. 



So, again, the Anastatica hierochuntica, or " Rose 

 of Jericho," a small annual with rounded pods, which 

 frequents sandy places in Egypt, Syria, and Arabia, 

 when dry, curls itself up into a ball or round cushion, 

 and is thus driven about by the wind until it finds a 

 damp place, when it uncurls, the pods open and sow 

 the seeds. 



These cases, however, in which seeds are rolled by 

 the wind along the ground, are comparatively rare. 

 There are many more in which seeds are wafted 

 through the air. If you examine the fruit of a 

 Sycamore you will find that it is provided with a 

 wing-like expansion, in consequence of which, if there 

 is any wind when it falls, it is, though rather heavy, 

 blown to some distance from the parent tree. Several 

 cases are shown in Fig. 47 ; for instance, the Maple a. 

 Sycamore b. Hornbeam d. Elm e, Birch / Pine^; 



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