STUDIES OF SEED-PLANTS 229 



the nuts are ripe and attractive to squirrels the burs split 

 open and scatter the nuts on the ground beneath the trees. 

 Obviously the spines were not made to protect the nuts from 

 squirrels, as some books assume, for the spines are not hard 

 until the nuts are ripening, and before that time no squirrel 

 would care for them. What then is the explanation? It 

 appears to be this, that like other modified structures, the 

 spines originally appeared without any regard to possible 

 use, and the splitting habit of the chestnut-bur has made it 

 impossible for them to become useful. If such spines had 

 developed on fruits which do not split and discharge their 

 seeds, we can imagine that they might have been of some 

 advantage and have become a useful adaptation as a pro- 

 tection against gnawing animals. There are many similar 

 cases among animals and plants where structures may at first 

 sight appear to have a use, but closer study shows us that 

 they are not useful adaptations. 



If structures appear without any reference to use, and prove 

 to be actually harmful, the plants which possess them will 

 probably disappear in time. For example, if the spines on 

 some chestnut-burs had in any way interfered with the 

 complete development of seeds, the result would have been 

 that the trees having such harmful spines would long ago 

 have disappeared, while the trees without them would have 

 perpetuated their kind, and we should now have only trees 

 producing spineless chestnut-burs. But the fact that the 

 spines continue to exist without serving any use suggests 

 that they are neither harmful nor useful, but simply harm- 

 less or neutral. There are many such harmless structures 

 among animals and plants. 



The above discussion will suggest that the student of 

 biology who is interested in adaptations of animals and plants 

 must not expect to find an evident use for everything. Appar- 

 ently some things have use, and many things have none 

 evident at the present time. In some of the apparently use- 



