III.] WINGED SEEDS FREQUENT ON TREES. 69 



is called, or leaf of the flower-stalk, serves the same 

 purpose. 



In a great many other plants the same result is 

 obtained by flattened and expanded edges. A beauti- 

 ful example is afforded by the genus Thysanocarpus, 

 a North American crucifer ; T. laciniatus has a dis- 

 tinctly winged pod ; in T. curvipes 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 {Pastinacd). But though in these 

 cases the object to be obtained — namely, the dispersion 

 of the seed — is eiifected in a similar manner, there are 

 differences which might not at first be suspected. 

 Thus in some cases, as, for instance, the Pine, it is the 

 seed itself which is winged ; in Thlaspi arvense it is 

 the pod ; in Entada, a leguminous plant, the pod 

 breaks up into segments, each of which is winged ; 

 in Nissolia the extremity of the pod is expanded into 

 a flattened wing ; lastly, in the Lime, as already 

 mentioned, the fruits drop off in a bunch, and the 

 leaf at the base of the common flower-stalk, or 

 "bract," as it is called, forms the wing. 



In Gouania retinaria of Rodriguez the same object 

 is effected in another manner ; the cellular tissue of 

 the fruit crumbles and breaks away, leaving only the 

 vascular tissue, which thus forms a net inclosing 

 the seed. 



