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ginning about the first of July and ending about the first ot beptem- 

 ber, while September is usually a wet and warm month. In watching 

 the remarkable growth of the cotton-woods, the professor's attention 

 was drawn to what he thought was a check in their activity in the lat- 

 ter part of the dry season, and the pushing of the terminal buds in 

 September and early October. He became deeply interested in what 

 he regarded as an abnormal condition, and watched with great care 

 until he was convinced that a new, or second tube of wood was formed 

 during this second growth. To test the matter fully he examined 

 cross-sections of some branches whose age he knew, and found that 

 the number of concentric rings exceeded the number of years they 



had been growing. 



In 1877 the dry season set in earlier, commencing about the 20th 



J 



This year was pe- 



culiarly well suited to testing the truth of second growth, as the dry 

 season was succeeded by wet and warm weather. As soon as frost 

 set in and vegetable growth had ceased, he made cross-sections of 

 several young branches and found that two distinct tubes of wood 

 had been added during the year. 



In further proof of the second growth hypothesis, I add the obser- 

 vations and experiments of Desire Charnay, who is now exploring 

 the ruins of Central America. He had grave doubt as to the great 

 antiquity assigned to some of the ruins that had been laid bare ; and 

 he learned, moreover, that the conclusions had been arrived at by 

 counting the rings in the cross-sections of large trees which had grown 

 upon the ruins, some of which exhibited rings enough to indicate that 

 the trees were 2,000, 2,500 and even 3,000 years old— calculating upon 

 the basis that one ring is made in a jean Mr. Charnay, had liis atten- 

 tion drawn to the investigation of the one ring theory in cutting down 

 a sapling which he knew to be eighteen months old, and on whose 

 cross-section he counted 40 concentric rings, making more than two 

 for every month of the plant's life. These observations were followed 

 up by Mr. Charnay, with the same comparative result, /. e., that more 

 than one tube of wood is made during the year ; hence he was forced 

 to the conclusion that no reliance could be placed upon that mode of 

 determining the date of the ruins. 



On a careful examination of the mangrove I was led to the belief 

 that exogenous growth in regions of no frost is very different from 

 that in the regions of frost, where most of our trees make but one 

 distinct ring, I am sure that most of them during some seasons make 

 indistinct rings. 



The mangrove puts forth a very vigorous growth, then ^rests appar- 

 ently from exhaustion, having formed terminal buds in all its branches. 

 After a short period of rest it pushes its buds and a new growth takes 

 place ; then, after another period • of great activity, there ensues 

 another rest, and so on< Tn each case a new tube is formed, so that 

 two or many may be made in a year. 



I have procured from Southern Florida and Southern Texas speci- 

 mens of many sorts, all of which confirm my belief in the hypothesis 

 that our exogens in regions of frost, as well as in the Tropics may, 



