8. t , __ 



birds, etc., scatter seeds and fruits. This is done in two ways: 

 (a) Where the fruit or seed is edible as in the black night shade, 

 cherry, poison ivy, seed of dandelion, thistle, etc., crows scatter 

 large numbers of seeds of the poison ivy. Millions of these 

 poison ivy seeds are annually consumed by birds. Large num- 

 bers of seeds of the dandelion, thistle, foxtail are consumed by 

 birds some of these are accidentally scattered in this way. Birds 

 are undoubtedly useful, however, in destroying large numbers 

 of weed seed. The colored fruits usually have hard seeds so 

 that they can pass the digestive tract of birds uninjured, (b) 

 In the second type the seeds cling to animals. Many of our 

 weeds have excellent contrivances for such dissemination. We 

 will mention in this connection the cocklebur. Each cocKlebur 

 has two so-called seeds. The bur is provided with hooks tna 

 cling to any passing animal and I have seen them scattered for 

 miles. The Burdock, another plant of the same family, has num- 

 erous seeds in a head; the hooked appendages get in the hair, 

 tails of horses, cattle, etc., where they form balls and thus the 

 seed is scattered. The Spanish needle or boot jack of the same 

 family has a flattened seed with two slender pointed bodies that 

 are barbed downwardly like grappling irons ; these cling to pass- 

 ing animals and carry the seed. Another weed, the Tick Trefoil, 

 belonging to the Pea family has a pod containing several seeds, 

 this pod breaks up into separate pieces when ripe, each contain- 

 ing a single seed. The pod is provided with hairs that are hooked 

 and so clings to animals. When removed the seed has often trav- 

 eled a long distance with the animal. Many other seeds of this 

 family like Licorice may be mentioned. Weeds with similar 

 contrivances are found in members of the Borage family, like 

 Hound's tongue, stickseed, etc. 



Explosive Properties. The seeds of a few weeds have explo- 

 sive properties. The seeds of the common yellow field sorrel has 

 a straight pod which, when mature and touched, shoots out the 

 seed like shot from a gun. The pods of certain vetches contract 

 and twist when mature, forcing the seed out. Contraction of 

 capsule of the three-seeded mercury scatters the seed, throwing 

 it some distance. This method of scattering can be observed bet- 

 ter on such a plant as the common Castor oil bean. 



Seeds Burying Themselves. A few of our weeds bury their 

 seed, but the needle grass growing on our dry sterile hills has 

 a sharp point to its "fruit," with small hairs which point obli- 

 quely upward. There is also a long awn to the fruit, this is sen- 

 sitive to moisture, it contracts when dry and straightens out 

 v hen moist and in this way buries the seed. 



