18 BULLETIN OF THE NATURAL HISTORY SOCIETY. 



balanced, even the light convection currents of a hot summer 

 day may raise them up to considerable heights, whence they may 

 be widely spread. These light plumes form the most efficient of 

 all the modes of locomotion. Most weeds owe a part at least of 

 their success to them, and the family Compositii? owes its great 

 predominance in part to the fact that the collection of the 

 flowers into heads and their protection by the involucre has set 

 free the calyx to form the pappus, giving to each single seed one 

 of the most effective of known disseminating structures. 



The plume or hairs may be formed of the sterile flower stalks 

 of a cluster, as in the " smoke bush ; " from the fruit stalk as in 

 Typlia ; from the calyx as in compositte, from the style as in 

 Geuvi and Clematis ; from the wall of the ovary ; from the seed- 

 coats as in cotton and milkweeds ; from the funiculus as in 

 willows. In rare cases the filro- vascular forms after decay of 

 the soft tissue a light frame easily blown away. 



6. The stalks of seed-pods may ripen elastically so that 

 when gusts of wind shake the pods, the seeds are hurled out 

 especially by the recoil. In these cases, the seeds, which are 

 small and smooth, are early loosened in the pods and the latter 

 open not at the bottom or along the sides but at the top, and in 

 such a way that they form smooth grooves along which the 

 seeds as they are hurled out are guided at such an angle that 

 they ai'e sent to the greatest distance. This is one of the 

 commonest modes of locomotion among herbs, and occurs 

 according to Hildebrand in Scro2)hulariacere, CampanuJacece, 

 Papaveracece, Prwiulacecv, C aryopliyllacew . It may be well 

 seen in the common poppies. This shaking of the stalks and 

 their sudden recoil may be brought about also by passing animals, 

 and probably the bladdery pods of some plants as Staphyllea, 

 etc., may assist this mode of locomotion by giving the wind a 

 larger surface to work against. 



The wind may also assist in locomotion by driving 

 floating seeds over lakes or the ocean either by blowing 

 directly against them, or by creating surface currents 

 which carrv them. 



