i68 THE POPULAR SCIENCE MONTHLY. 



as " elaters." They move with great vigor, and probably serve the 

 same purpose. 



In much more numerous cases, seeds are carried by the wind. For 

 this, of course, it is desirable that they should be light. Sometimes this 

 object is attained by the character of the tissues themselves, sometimes 

 by the presence of empty spaces. Thus, in Valerianella auricula, the 

 fruit contains three cells, each of which would naturally be expected 

 to contain a seed. One seed only, however, is developed, but, as may 

 be seen from the figure given in Mr. Bentham's excellent " Handbook 

 of the British Flora," the two cells which contain no seed actually be- 

 come larger than the one which alone might, at first sight, appear 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 the 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. 12 ; for instance, the maple, a, sycamore, 5, 

 hornbeam, d, elm, e, birch, /*, pine, g, fir, A, and ash, ^, while in the lime, 

 c, the whole bunch of fruits drops together, and the " bract," as it is 

 called, or leaf of the flower-stalk, serves the same purpose. 



In a great many other plants the same result is obtained by flat- 

 tened and expanded edges. A beautiful example is afforded by the 

 genus TJiysanocarpus, a North American crucifer ; Th. lacmiatub has 

 a distinctly winged pod ; in T. ciirvipes the wings are considerably 

 larger ; lastly, in T. elegans and T. radians the pods are still further 

 developed in the same direction, T. radians having the wing very 

 broad, while in T. elegans it has become thinner and thinner in places, 

 until at length it shows a series of perforations. Among our common 

 wild plants we find winged fruits in the dock [Rumex) and in the 

 common parsnip (Pastinaca). But though in these cases the object 

 to be obtained namely, the dispersion of the seed is effected in a 



