DISPERSAL OF FRUITS AND SEEDS 



221 



device which increases the surface without greatly in- 

 creasing the weight of the seed, e. g. : 



(i) Minute spores x of Fungi, Mosses, and Ferns, and also 

 microscopic plants. The frequent occurrence of moulds on 

 organic substances is due mainly to the ease with which 

 their abundant spores are carried in the air. 



(2) Minute seeds, as of Orchids, which are rendered 

 lighter still in proportion to bulk by a light, loose, outer 



8 r 9 



Fig. 156. Fruits and Seeds dispersed by the Wind. 1, seed 

 of Orchid, much magnified ; 2, seed of Willow ; 3, seed of Pine ; 

 4, achene of Clematis ; 5 a, fruit of female flower of Coltsfoot ; 

 5 b, barren fruit of male flower of Coltsfoot ; 6, mericarp of Hog- 

 weed ; 7, samara of Elm ; 8, fruit of Hornbeam ; 9, rolled pod of 

 Medicago. 



coat (Fig. 156, 1). Heaths also have extremely small 

 wind-dispersed seeds. 



(3) Seed-Parachutes. Small seeds, even though larger 

 than those mentioned above, may bear tufts of hairs 

 serving as a parachute, e. g. Willows (Figs. 156, 2 and 157), 

 Poplars, Willow Herbs (Epilobium) (Fig. 158, 2), and Cotton 

 (the cotton fibres of commerce being highly developed 

 seed-hairs). 



(4) Fruit-Parachutes. The small fruits of many Com- 

 positae and other plants have a pappose calyx, e. g. 



1 Spores are minute reproductive cells capable of growing into 

 new plants. Fungi, Mosses, and Ferns never produce true seeds. 



