6i6 



ring in woody plants depends upon the amount and kind of leaf activity. 

 This has been thoroughly treated in forestry literature. Every considerable 

 interruption in the activity of the leaf apparatus makes itself felt in the 

 wood and can lead to the omission of wood formation in one side of the 

 tree, or at the base of the trunk and in the root. If the cambium, which had 

 been active in the spring, is incited to renewed increase in the same year 

 after a period of inactivity, it begins the formation of a new spring wood 

 which passes over into autumn wood, sometimes more slowly, sometimes 

 more quickly. In this way a new, normal, annual ring is produced. In 

 such cases are found semi-circular double rings, or others encircling the 

 whole girth of the trunk. 



We owe exact studies on this subject to Kny^, who determined espe- 

 cially clearly in Tilia parvifolia that, after the sprouting of the buds on 

 shoots which had been entirely defoliated by caterpillars, a second annual 

 ring was formed. The boundary between the newly formed spring wood 

 and the wood ring produced before defoliation is sharp. In Ratzeburg's- 

 study we find repeated examples of the dependence of the formation of the 

 annual ring on the time of defoliation. Since diifcrent insects can cause 

 complete defoliation, at different times of the year, a weakening of the 

 growth of wood is found sometim.es in the same year, but, at other times, 

 not until the following year (when the deposition of reserve substances is 

 scanty). 



In 1886, I was able to add the action of frost to the causes which can 

 bring about the formation of false annual rings. In 1895 R. Hartig^ pub- 

 lished a treatise in which he described frost rings in the oak and fir and 

 considered also a different mechanical effect, viz., a drooping of the shoots 

 due to a loss of turgidity. This bending of the shoots became permanent 

 and could be found the following year. The drooping can also occur as a 

 result of the destruction of the pith parenchyma. In the last edition of 

 Hartig's text book*, frost rings from the wood of a pine and of a spruce 

 are illustrated with the remark "in older parts of the trunk of the pine it 

 was found that a so-called double ring was produced in each year of late 

 frosts. I later confirmed the fact also in spruces and other conifers, that 

 a late frost not only injuries the youngest shoots but even produces the 

 'double rings' formed in parts of the trunk which were ten years old." 



O. G. Petersen^ describes and illustrates a similar disturbance in the 

 structure of the annual ring of beech trees which had suft'ered severely from 

 frost on the 17th to i8th of May, 1901, in Holland. Nordlinger^ had 



1 Kny, L., iiher die Verdoppelung des Jahresringes. Sep. Verhandl. d. Bot. Ver. 

 d. Prov. Brandenburg- 1879. Here also discussion of earlier theories. 



2 Ratzeburg, Waldverderbnis, I, p. 160, 2.S4; II, p. 154, 190. 



8 Hartig, R., Doppelringe als Folge von Spatfrost. Forstl. naturw. Zeitschrift 

 1895, p. 1-8. 



4 Lehrbuch der Pflanzcnkrankheiten. Berlin, Springer 1900, p. 220, 221. 



n Petersen, O. G., Natterfrostens virkning paa Bogens ved. Sep. Det forstlige 

 Forsogsvaesen, I. 1904. 



6 Nordlinger, Die fetten und die mageren Jahre der Baume. Kritische Blatter 

 C. Forst- und Jadgwissenschaft, 1865, Vol. 47, Part 2. 



