Killing of Plant Tissue by Low Temperature 215 



tissue is generally most tender, the tissue near the base of the tree is 

 most hardy. 



Selby^ observed that the great tenderness in the early part of 

 the winter is probably due to a greater moisture content. He ob- 

 served that the cambium in winter during the time when plants are 

 very hardy, is in a much dried out condition and in normal seasons has 

 to some extent reached this condition by the time of the early freezes, 

 but in seasons like that one preceding the winter of 1903-4 it is still 

 in a somewhat succulent condition when the early freeze comes. 



It is well known that seeds in a dry condition will withstand 

 very much lower temperature than when they have absorbed moist- 

 ure. Thus Schaffnit^ reduced the germination percentage of wheat 

 from 100 to 40 by soaking it in water for eight hours at room tem- 

 perature. In twigs it is probable that a dry condition is essential 

 to the hardiness of the cambium. Shutt^ and also Allen^ seem to 

 find a relation between moisture content and hardiness of apple 

 twigs. However, it does not seem that the increase in hardiness 

 of other tissue than cambium, at least of cortex, during early winter 

 can be explained by a decreasing moisture content. 



During the winter of 1912-13, beginning November, twigs of 

 apple, peach, plum and cherry were scraped, the cortex ground, 

 weighed carefully, evaporated to dryness in a water bath (to which 

 later glycerine was added to raise the boiling point in the water 

 jacket and thus raise the temperature), and weighed at intervals of 

 two to three days until a constant weight was reached. Samples 

 were taken again in January and again in May. No samples were 

 taken when the tissue was frozen, since then the percentage of mois- 

 ture would be smaller. The evaporated moisture could not be re- 

 placed from below. The following table gives the results: 



lOhio Agr. Exp.Sta. Bui. 192, 1908. (Bibl. No. 101). 



2Mitt. Kaiser Wilhelm Inst. Laxidw. zu Bromberg. VoL 3, No. 2, pp. 93-113, 1910. 

 (Bibl No. 98). 



'Procs. and Trans. Roy. Soc. Canada, ser. 2, Vol. 9. pp. 149-163. (Bibl. No. 104.) 

 4Master'8 Thesis, Iowa Agr. Exp. 8ta. (Bibl. No. 2). 



