ADAPTATIONS 255 



STRUCTURAL ADAPTATIONS 



Changes in structure to meet special conditions of growth may 

 be of several different types. 



One of these, which is often cited as an example of adaptation 

 (in this case, the term is used with a significance quite different 

 than that in which it is being used here) is that of the development 

 of unusual and often fantastic shapes of flowers, which are so 

 related to the anatomy of certain species of insects that visit these 

 flowers in search of nectar, that provision for the cross-fertiliza- 

 tion of the plants is insured, in that the pollen from the anthers 

 of one flower becomes lodged on the body of the insect as it is 

 withdrawing from the flower in such a way that it comes in con- 

 tact with the pistil of a second flower as the insect enters it. Such 

 flowers often have such peculiar shapes and lengths of nectar tubes, 

 etc., that only a single species of insect, whose anatomical shape is 

 " adapted " to that particular blossom shape can enter the flower 

 in its search for nectar. It is clear that this form of " morpho- 

 logical adaptation " is a highly specialized one, which can only be 

 the result of a long process of evolutionary development. It is 

 obvious that the plant cannot possibly possess a mechanism, or 

 ability, to alter its flower form in order to make it conform to the 

 shape and length of the proboscis, or other body parts, of a par- 

 ticular species of insect. Either the insect or the plant, or both, 

 must go through a process of evolutionary development in order 

 to arrive at this form of mutual " adaptation." 



A form of true morphological adaptation (in the sense in 

 which we have been using the term) is exhibited by many species 

 of plants, which are provided with many more buds, or growing 

 points, than ever actually begin to grow. For example, the single 

 plumule which develops from a germinating wheat embryo has at 

 its upper end a hundred or more tiny growing points. At the 

 proper stage of its growth, several of these tiny buds begin to 

 grow into individual separate stems, and the new wheat plant thus 

 produces several stems from one seed and root system, a process 

 known as the " stooling." The number of stems in a single 

 " stool " depends upon the number of the potential growing points 

 which are stimulated into growth. It varies from only two or 

 three up to as many as thirty or forty, and is apparently con- 

 trolled by the favorable or unfavorable conditions of climate or 



