296 Report of the Botanical Department of the 



Low temperature and excessive or late nroivth as factors in production 

 of crown-rot. — As stated above these factors have not been experi- 

 mentally demonstrated as causes of the disease but their causal rela- 

 tion was chiefly inferred from observations made in a large number 

 of affected orchards. The observed facts show that the initial in- 

 juries which result in crown-rot occur in winter and that rapidly 

 grown trees are most subject to the disease; they indicate that bark 

 in certain stages of its life history is more susceptible to the injury 

 than in others, and also that the increase in diameter of a tree trunk in 

 relation to itsformerdiameter, as well as the premature checking of bark 

 growth, probably have acausal relation to thcoccurrenceoftheinjuries. 



According to Goppert^ bark on trees and shrubs is cleft by the 

 drjdng out of winter-injured bark after thawing and not by the 

 freezing of abundant sap as is commonly held; and that clefts in 

 crotches are caused by the wind vv^hile the tissues are frozen and 

 brittle. These injuries are said to be especially common on Prunus 

 and Pyrus. 



He found that frequently injuries occurred in the medullary rays 

 and presumably in the inner phloem for he stated that in case the 

 affected parts survive, discolored tissues which are subsequently 

 covered by new annual rings, mark the year of injury. From his 

 observations and remarks made about those of several earlier inves- 

 tigators, it seems as though he had in mind appearances like 

 those showTi on Plate VI of the above paper on crown-rot, and the 

 thin discolored line on the left side of Plate XX and figures 1, 6 and 

 7 on Plates XXVIII and XXIX of the present paper. 



Goppert held that plants are not susceptible to winter-injury 

 because they contain a superabundance of sap but on account of 

 their stage of development or state of vitality. 



Some of the older observations and experiments on this phase of 

 the subject are very interesting. They are to be found in both horti- 

 cultural and botanical literature. A few of the more pertinent ones, 

 with the conclusions reached, are worth noting on account of the 

 light they throw on the above field observations and because of the 

 diversity of opinion regarding factors involved in the production of 

 winter injuries. 



W. H. de Vriese^ in a discussion on " Some principles of vegetable 

 physiology, bearing on the culture of plants " attriljutes clefts in 

 trees to the absorbing action of roots in winter: " the rising fluid 

 ascends in trunks of trees and often causes large trees, the expansion 

 of which is prevented by the cold, to split from top to bottom." 



1 PI. R. Goppert. Ueber die Warmo-Entwicklung in den Pflanzen, deren Gefrieren 

 und die Schutzmittel gegen dasselbc. pp. XVI-|-273. 1830. 

 Breslau. 

 ^ W. H. de Vriese. Some principles of vegetable physiology, bearing on the culture 

 of plants. 



Gard. Chron. Agrl. Gaz. 1854:597. 1854. 



