Killing of Plant Tissue by Low Temperature 147 



STUDIES ON THE KILLING OF TISSUES OF HORTICULTURAL 

 PLANTS BY LOW TEMPERATURE 



The work to be reported in this paper was begun during the 

 season of 1904-05. At that time the studies concerned only the 

 effect of certain cultural methods on the hardiness of the fruit buds 

 of the peach under climatic conditions that prevail in the southern 

 half of Missouri. Later they were extended to include the possible 

 effect that a large amount of potassium or other mineral elements 

 in the soil might have on the ability of the peach fruit buds to with- 

 stand,-;old. 



In taking up this problem it is necessary to distinguish between 

 some of the various phases of injury from cold. Various writers 

 have mentioned observations on frost cracks, that is, a formation 

 of cracks in the wood of the tree during freezing weather. Caspary^ 

 showed that the formation of these cracks is due to a greater contrac- 

 tion of the tissue of the tree tangentially than radially. Later, 

 Miiller-Thurgau^ made a very careful study of these cracks and 

 confirmed Caspary's opinion, but showed that this great contraction 

 tangentially is due rather largely to the shrinking of the cells of the 

 medullary rays. These medullary rays extend in lines from the 

 center out, and are made up of rather thin walled cells separated no- 

 where by very rigid tissue. These rays separate wider strips of 

 rigid tissue extending in a wedge shape from the surface to the center 

 with no lines of more pliable tissue crossing them. Then where the 

 cells of the medullary rays contract on the passage of water into the 

 intercellular spaces to form ice crystals, shrinking toward the center 

 is limited to the rate of shrinking of the strong wedges of rigid tissue, 

 while radially there is the shrinking of the rigid tissue and the more 

 rapid shrinking of the medullary ray tissue. 



There seems to be another type of injury' to the wood of trees, 

 especially the small twigs, due apparently to the fact that during 

 a long cold period much moisture will be lost from these twigs that 

 can not be replaced because of the frozen condition of the conducting 

 tissue. Thus death will result from the great loss of water from the 

 twigs by evaporation. Killing of this kind seems to be worse in 

 regions with prevailing strong winds and continuous low winter tem- 

 perature. Thus Allen* finds a rather direct correlation between the 



'Dot. Zelt. Vol. 13. pp. 449-62. 473-82. 489-500 (Blbl. No. 17); Hot. Zolt. Vol. 15, pp 

 329-35. 343-50. 361-71 (Bibl. No. 10). 



2Landw. Jahrb. Vol. 15. p. 4.\3. 1HH6 (Hlhl. No. 78). 



3A. Nolison, Wyo. Agr. Exp. Sta. Hul. 15. 1893. (Blbl. No. 81). 



Maator"8 Thesis. Iowa Agr. Exp. Sta. (Blbl. No. 2). 



