6 KOTES ON THE BALD CYPRESS. 



among them where the variations arising from the change of position of 

 the trees occur with the immediateness and distinctness that they do here. 

 In the chestnut-oak, for instance, the bark of the swamp variety becomes 

 smoother and thinner, and contains less tannin, than in the highUmd forms ; 

 but the changes are relatively slight and quite irregular, never presenting 

 the close relation to the conditions of environment that is given in the case 

 of the cypress knees. It has been shown also, by the researches of Mr. 

 DeFriese, assistant in charge of the timber studies made by the Survey, 

 that the hemlock is never found in Kentucky on any other soils except 

 those produced by the decay of sandstones and conglomerates, or more 

 than a few hundred feet from running water, which serves probably to 

 give a certain dampness to the air; but narrowly limited as this species 

 is, it does not give anything like the clear proof of the immediate effect 

 of conditions on the characters of an organic form that is afforded by 

 the swamp cypress. It is doubtful if, in all our American forest trees, 

 another instance can be found where a slight change of surroundings can 

 bring about such important modifications of the conditions of life as in 

 the case of the cypress. 



These processes termed knees evidently serve very much to extend the 

 area over which the tree can maintain itself There can be little doubt 

 that by it the tree has gained access to at least thirty thousand square 

 miles of area in the southern part of the United States, from which it 

 would otherwise have been debarred. 



I have been unable to find any account of other species of trees having 

 such knee-like processes. Several species of our ordinary timber trees are 

 apt to make nodulose projections from their main roots; and wlien they 

 grow in swampy ground are apt to keep their roots rather near the sur- 

 face; but none of them have developed such specialized structures as are 

 fomid in the Taxodium, and none of them have anything like the jjower 

 of adapting themselves to such varied conditions of humidity. So far as 

 is known to me, the Taxodium is the only tree that is able to occupy 

 positions varying from veiy wet swamps to rather dry uplands. It is not 

 too much to say that its range of station, so far as actual conditions go, 

 is about double that of any other forest-tree belonging to the Xorth Amer- 

 ican flora. 



It is a well known fact that the ancestors of our Taxodium can be clearly 

 traced back to the time of the miocene tertiary. At that time a closely 



