20 BULLETIN" 272, U. S. DEPARTMENT OF AGRICULTURE. 



headings. Each of the two forms, however, within itself presents 

 real variations in leaf, branch, bark, and wood. 



There are indications that the varietal form (var. imbricarium) , 

 which is more abundant over the Atlantic Coastal Plain than else- 

 where, is undergoing a gradual botanical segregation during its 

 assumed northward migration from Florida, and has been since 

 the close of the glacial period. Progress hi segregation is necessarily 

 slow on account of the heaviness of the seed and its exacting moisture 

 requirements for successful germination. Evidence points clearly 

 to soil conditions, particularly acidity and drainage, as fundamental 

 factors causing the botanical variation of cypress. The range of 

 the imbricate form, so far as at present known, is generally coincident 

 with the limits of the Atlantic Coastal Plain, but extends southward 

 into northern Florida and westward to Alabama. The main species, 

 on the other hand, finds its most congenial home along the Gulf 

 Coast and up the Mississippi Valley in the deep alluvial soils. 



OCCURRENCE. 



The close restriction of cypress to very wet situations suggest 

 two explanations: (1) That the species requires much water and is 

 in reality a semiaquatic or mud-inhabiting species, or (2) that it 

 has been forced to these unfavorable situations because of inability 

 to compete with species better adapted to occupy the more favorable 

 uplands. 



Close observations on young cypress agree in furnishing evidence 

 that, in its early stages, cypress is very exacting and successfully 

 establishes itself only in situations of very abundant moisture. 

 Subsequently, however, seedling growth is noticeably more rapid 

 on better drained situations. These observations lead to the con- 

 clusion that in extremely wet situations cypress, in a greater or 

 less degree, is tolerating conditions not generally favorable to the 

 normal thrifty growth and development of the tree. In other 

 words, the inherent soil and moisture requirements of cypress after 

 its earliest stages are to be looked upon as very similar to those 

 of many of the hardwood timber trees which thrive best in a deep, 

 loose, well-drained, fresh, rich, sandy or clayey loam, containing 

 humus and available mineral food, and well supplied with soil 

 moisture. 



Broadly speaking from a geological standpoint, cypress therefore 

 belongs characteristically to young lands. Cypress is the dominating 

 tree in the forests of the alluvial lands of the South. It advances 

 slowly, but ahead of all other trees, as river and sea marshes gradually 

 build up, nourishes in the deep alluvial soils submerged for a portion 

 of the year, and later is driven out by the competition of hardwoods 

 as the lands are further built up and become drained. 



