lOo THE AMERICAN MONTHLY [April, 



the digestive action when swallowed by birds ; and {d) of a dull, 

 brownish color and minutely furrowed surface presenting a re- 

 markably sandy aspect when seen without the microscope. 



What is the significance and the cause of evolution of these last 

 features, which constitute the principal microscopical peculiarities 

 of the specimen ? Apparently they must be related to the dissem- 

 ination by agency of birds, and in this respect they may be im- 

 portant in either one of two exactly opposite ways. The obscure 

 and sandy appearance would evidently render it difficult for the 

 birds to find and carry oft" the seeds sufficiently to prevent crowd- 

 ing in the immediate neighborhood ; and this may account for the 

 habit of the plant to overstock, to an exceptional degree, fields in 

 which it has become established. On the other hand, they seem 

 adapted to bird-dissemination to a moderate degree ; and the ex- 

 tent to which this actually occurs and is of service to the species 

 is an interesting question for future investigation. 



Fruits that are highly specialized for bird-dissemination, such 

 as most of the familiar berries, are large enough to be easily found 

 and to be worth the trouble of eating, and are of showy colors, 

 red, which seems specially attractive to birds and to some other 

 fruit-eating animals, blue, blackish, or white. A few handsome 

 and showy seeds appeal likewise to the vision of the birds ; but 

 being hard and probably not digestible they have been considered 

 unserviceable to the birds, and attractive only to young and inex- 

 perienced ones that had not 3'et learned their uselessness, and that 

 are, therefore, by misapplying the teachings of instinct that attrac- 

 tive-looking fruits are good to eat, easily duped into taking and 

 swallowing what will prove useless to them. But is there any 

 proof of this in the known facts, and is it probable that the instinct 

 of the birds would be thus misled sufficiently to cause the high 

 degree of specialization already attained in such seeds.'' I think 

 not. It seems far more likely that the birds, not misguided, but 

 led by a true instinct, swallow these hard morsels not as food, nor 

 in vain, but as mechanical aids to digestion, as birds are known to 

 do in some cases, having learned by experience that the nourish- 

 ing food serves them better in such company. This theory would 

 account for the swallowing of these indigestible morsels, even 

 when, as in the present case, they do not look like edible berries, 

 and also for the evolution, as yet unexplained, of the granular- 

 looking surfaces variously wrinkled, furrowed, honeycombed, 

 pitted, tubercled. or spiny, that ornament many kinds of minute 

 seeds and make them favorite microscopic objects. In case of 

 tiny birds, at least, the minutely-roughened surface would add 

 perceptibly to the value of these insoluble particles as triturantsor 

 local irritants, while the sculpturing of the surface may even assist 

 somewhat in finding and recognizing the objects. These details 

 are probably more visible to a bird closely searching for food than 

 to our more distant view, since the size of the retinal image would 

 increase rapidly with the nearness of the eye to the object. 



