SEEDS 



- 5293 



SEEDS 



SOME OF NATURE'S MEANS OF SEED DISPERSAL, 



(a) Winged seed of the maple; (b) burs of "sticktights ;" (c) seeds of Spanish needles; (d) dan- 

 delion seeds; (e) burdock seeds; (/) winged fruits (seeds) of American elm; (g) tumbleweeds 

 blown by the wind. 



conditions, are brought from their shelter at 

 the proper time. 



Dispersal by Wind. The wind is the chief 

 agent in scattering seeds. Some dustlike seeds, 

 like those of the orchid, float in the air, and 

 others are provided with downy, tufted para- 

 chutes or wings. The tufted seeds of the 

 thistle and dandelion and those imbedded in 

 soft wool and silken hair, such as the cotton, 

 poplar and milkweed seeds, are detached from 

 their beds by the dry winds and warm sun and 

 are blown long distances. The seeds of the 

 maple, elm and ailanthus are equipped with 

 membranous wings, and in others the fanlike 

 petals of the dry calyx form the sails or para- 

 chutes which carry them to distant places. The 

 wings and parachutes of some seeds become de- 

 tached after the journey through the air; others 

 remain on the seed and serve to fasten it in 

 some favorable place for germination. 



Whole clusters of fruits containing seeds, such 

 as the white pine cone, are also blown from 

 place to place. The smooth, light fruits of 

 tropical plants, like the "steppe witches," are 

 rolled for miles over the level, barren steppes 



until they fall into some crack in the clay or 

 are lodged in a hole, where the seed germinates 

 and produces a new plant. In such plants as 

 the tumbleweed, the stalk parts from the roots 

 when the seeds are ripe, and as the plant is 

 blown from place to place it scatters its thou- 

 sands of seeds. 



Perhaps the most curious and interesting 

 natural seed scatterers are the "sling fruits" 

 and "catapult fruits." In the former the tis- 

 sues around the ripened seeds become highly 

 tense and burst their outer covering, which then 

 contracts with a violent jerk, forcibly expelling 

 the seeds as from a sling. In some plants the 

 seeds are expelled by the drying up of the pod 

 or the spiral twisting of the valves of the fruit. 

 The catapult fruits, such as the light pods of 

 the poppy and morning glory, are open at the 

 top, and when the stalks are bent or swayed to 

 and fro they rebound, flinging the seeds in all 

 directions from the top of the pod. 



Dispersal by Water. Water and moisture are 

 also important agents in the dispersal of seeds. 

 Water plants, such as the lotus and also some 

 varieties of palms, have floating seeds contain- 



