DISPERSAL OF SEEDS 



173 



oxalis is common in several species in the wild and in 

 cultivation. One of them is known as wood sorrel. Figure 

 250 shows the common yellow oxalis. The pod opens 

 loculicidally. The elastic tissue suddenly contracts when 

 dehiscence takes place, and the seeds are thrown violently. 

 The squirting cucumber is easily grown in a garden (pro- 

 cure seeds of seedsmen), and the fruits discharge the seeds 

 with great force, throwing them .many 

 feet. 



Wind Travelers. Wind - transported 

 seeds are of two general kinds : those 

 that are provided with wings, as the flat 

 seeds of catalpa (Fig. 251) and cone-bear- 

 ing trees and the samaras of ash, elm, 

 tulip-tree, ailanthus, and maple ; and 

 those which have feathery buoys or para- 

 chutes to enable them to float in the air. 

 Of the latter kind are the fruits of many 

 composites, in which the pappus is 

 copious and soft. Dandelion and thistle 

 are examples. The silk of the milkweed 

 and probably the hairs on the cotton seed 

 have a similar office, and also the wool of 

 the "cat-tail. Recall the cottony seeds of 

 the willow and poplar. 



Dispersal by Birds. Seeds of berries and of other 

 small flesliy fruits are carried far and wide by birds. The 

 pulp is digested, but the seeds are not injured. Note how 

 the cherries, raspberries, blackberries, June-berries, and 

 others spring up in the fence rows, where the birds rest. 

 Some berries and drupes persist far into winter, when they 

 supply food to cedar birds, robins, and the winter birds. 

 Red cedar is distributed by birds. Many of these pulpy 



FIG. 251. WINGED 

 SEEDS OF CATALPA. 



