76 



PROPAGATION OF PLANTS. 



distribution by the wind. Others have hooked awns on 

 the outside of their seed-vessels, as on those of the Bur- 

 dock (Lappa) and Beggar-ticks (Bidens), which become 

 attached to any rough surface like the hide of animals or 



wool of sheep, and by such 

 means become widely dis- 

 tributed. The seeds of many 

 kinds of trees are provided 

 with wing-like appendages, 

 those of the Elm having a 

 thin membrane passing nearly 

 or quite around, the edge of 

 the seed, as shown in figures 

 35 to 37. The Ash tree has 

 long, slender one to two celled 

 seeds with a wing on two 

 sides and the upper end 

 figure 38. The seeds of the 

 Maples are produced in pairs, 

 each pair the product of a 

 single flower, the membrane 

 of the wing growing inward 

 from its stem, as shown in 

 figure 39, which represents a 

 pair of the seeds of the Large- 

 Fig. SPACER MACROPHYLLUM. leaved California Maple (Acer 



macrophyllum) of natural size. 



In the Coniferce, or cone-bearing trees, the seeds of a 

 large majority of the species are winged, but in only a 

 limited number are these appendages of any assistance in 

 their distribution. In the seeds of the Great Tree of 

 California (Sequoia giganted), the Arbor Vitass (Thuya), 

 and closely allied species, the wings are firmly attached 

 to the seeds, consequently aiding in their extended dis- 

 tribution as they fall from the cones, but in many species 

 of conifers the wings are deciduous, readily parting 



