EFFECTS OF FROST ON TREES. 



205 



growing state that are charged with the 

 cambium or elaborated sap, containing the 

 elements of a new lnyex or stratum of wood. 

 So soon as this deposit is fairly made, the 

 tree quickly ceases to grow, and the little 

 sap in circulation contains comparatively 

 little more than water. In the latter part 

 of the month of June, I have seen the an- 

 nual concentric layer deposited in due form, 

 but yet in a soft, almost semi-fluid, state, 

 adhering imperfectly to the old wood, and 

 readily separated from both wood and bark. 

 The work of after growth for the season, 

 is to'consolidate and perfect this layer. This 

 done, the sap, highly charged with living 

 woody matter, ceases to flow ; and it is only 

 this unconsolidated living matter that is 

 highly susceptible to the chemical action of 

 frost. Except its protection by the bark, 

 it may well be supposed to be more tender 

 and susceptible, than the most delicate ex- 

 panded leaf of spring. 



This theory of M. Morren also makes 

 the true cause of the summer blight of pear 

 trees, more probable than any thing I have 

 seen, by an easy transition. It is well 

 known that on the living organism of plants 

 and animals, heat and cold seem to pro- 

 duce very similar injuries. It is equally 

 well known that the pear is a native of 

 countries not subject to the extremes of 

 heat or cold felt here. Suppose then the 

 tree is rapidly growing, and its new albur- 

 num is in the semi-fluid state of which I 

 have spoken, and suppose one of our unu- 

 sual hot days, or singularly cold nights, in 

 either case, is it unreasonable to suppose, 

 that chemical decomposition occurs in the 

 charged sap, and death is induced ? In 

 the laboratory great changes are produced 

 by a change of temperature, and it is rea- 

 sonable the like occurs in the laboratory of 

 nature. If something of this kind was not 

 intended, I am not aivare what Kenrick and 



others have meant in referring blight to a 

 stroke of the sun. 



In the human system, we know chemical 

 action often overpowers the vital action 

 in the stomach, and the fermentation of de- 

 composition prevents digestion. And rea- 

 soning from analogy, it may well be con- 

 cluded, that when the tree is fully charged 

 with cambium or vital sap, full of the ele- 

 ments of wood, and there comes an unusu- 

 ally cold night or hot day, or dry or wet 

 time, or there happens to the tree any other 

 accident, which weakens the vital action, 

 chemical action will take place, and a rapid 

 decomposition of the true sap ensue, ren- 

 dering that which should have formed wood 

 poison to the tree. It follows, therefore, 

 that the way to prevent blight, is to keep 

 the tree in good health, and as far as pos- 

 sible to prevent excesses of all kinds — es- 

 pecially excess in manure, and in moisture, 

 and cultivation ; andthat regularity should 

 be practised, and every operation well 

 timed. 



If a tree hitherto neglected, be power- 

 fully manured at midsummer, and especial- 

 ly if it be trimmed at the same time, death 

 may be expected. So of extra cultivation, 

 commenced after midsummer. Some soils 

 naturally produce great irregularities in the 

 growth of trees. This I know to be the 

 case with the rich limestone hills in the 

 northeast part of Ohio, where pear tree blight 

 is very common, and where it evidently 

 often occurs in the summer, and frequently 

 does not extend below the growth of the 

 season. That it does originate in the sum- 

 mer, is clearly proved by the facts related 

 by Lemuel Powell in No. 7 of the third 

 volume of the Ohio Cultivator, at page 52. 

 Mr. Powell moved part of a lot of pear 

 trees of the same age and condition, win- 

 tered alike, in the spring, from Jefferson 

 county to Meigs county. Those removed 



