BUR-TRAVELERS 



169 



soe. The cow is carrying 



agreeable as human food, and some of them have been greatly 

 enlarged or "improved" by the arts of the cultivator. 



331. Burs. Many seeds and fruits bear spines, hooks , 

 and hairs that adhere to the coats of 

 animals (Fig. 306) and to clothing. 

 The burdock has an involucre with 

 hooked scales, containing the fruits 

 inside. The clotbur is also an in- 

 volucre. Both are compositous plants, 

 allied to thistles, but the whole head, 

 rather than the separate fruits, is 

 transported. In some compositous 

 fruits the pappus takes the form of 

 hooks and spines, as in the "Spanish 

 bayonets" and "pitchforks." Fruits 

 of various kinds are known as "stick- 

 tights," as of the agrimony and 

 hound's tongue. Those who walk in the woods in late 

 summer and fall are aware that plants have means of 

 disseminating themselves. (Fig. 307.) If it is impossible 

 to identify the burs which one finds on clothing, the seed 

 may be planted and specimens of the plant may then be 

 grown. 



REVIEW. What advantage is it to the plant to 

 have its seeds widely dispersed? What are the leading 

 ways in which fruits and seeds are dispersed? Name 

 some explosive fruits. Describe wind-travelers. What 

 seeds are carried by birds? Describe any bur with 

 which you are familiar. 



NOTE. This lesson will suggest other 

 ; ways in which seeds are transported. Nuts 



are buried by squirrels for food, but if they 

 307. Stealing a ride. ^ not eaten they may grow The geeds of 



many plants are blown on the snow. The old stalks of weeds, standing 

 through the winter, may serve to disseminate the plant. Seeds are 

 carried by water down the streams and along shores. About woollen 



