210 



SCIENTIFIC AGRICULTURE. 



May, 19'21. 



strengths shows different conditions for different sea- 

 sons. A layer taken for examination in late autumn 

 shows that mueh water may be drawn from within the 

 cell without causing the death of the protoplasm, pro- 

 viding the resulting concentration in the said sugar so- 

 lution increases slowly. It is also shown that protoplasm 

 from which water has been drawn in the above manner, 

 or by freezing, is much more likely to be injured during 

 the process of assuming its original form. The more 

 water which is withdrawn, the greater is the danger 

 involved in the process. "One can therefore draw the 

 conclusion," says the author, "that protoplasm is more 

 susceptible to thawing than to freezing, and that it may 

 live through very severe freezing but may be killed dur- 

 ing the process of thawing." 



I have not been able to find any satisfactory explana- 

 tion as to why protoplasm varies in its ability to with- 

 stand the effects of the cleaving whicli takes place as a 

 result of the re-arrangement in its molecules or in what 

 manner a plant may undergo a change in its hardiness 

 through the effect of changed conditions. It is -well- 

 known that a living organism may to a certain extent 

 adapt itself to its pai'ticular conditions of life, and that 

 when a change in these conditions takes place, so that 

 it does not longer stand in full harmony with the new 

 condition, it seeks to adapt itself to these conditions pro- 

 viding the change is not too great or too sudden. Ac- 

 cording to Hedlund, when a plant is effected by low 

 temperature, and is able to witlistand freezing, a change 

 takes place in the finer organization of the protoplasm 

 so that it can better withstand an eventual re-arrange- 

 ment of its small particles or molecules. This greater 

 hardiness, it is shown, is realized only when the temper- 

 ature is as low as possible without causing the formation 

 of ice. 



By freezing, a plant or plant part does not become 

 more hardy, but on the contrary less hardy. Alternate 

 freezing or thawing during the winter or spring is, as 

 is well-known, much more injurious than is a steady 

 frost. It seems clear from these investigations that frost 

 hardiness is first and foremost dependent upon this 

 ability of the protoplasm to withstand the changes with- 

 in its small particles to which reference has been made. 

 Obviously then the problem of the practical grower 

 should be to provide if possible some means or some 

 conditions of growth which will increase the concentra- 

 tion of liquids within the cell, and thus lower the freez- 

 ing point. "This means" says Hedlimd. "consists in 

 the storing up of solubles and solids within the cell. 

 Pure water freezes under ordinary circumstances as 

 soon as the temperature reaches 32 dee. F. but when 

 this water contains some substance in sol'ition the freez- 

 ing point, as is well-known, drous. The increasing of a 

 solution's osmotic pressure bv twelve atmospheres cau- 

 ses the freezing point to sink 1.8 deg. F.. when the liquid 

 used consists of water. "Within the living cell of the 

 plant are alwavs to be found sohd^le substances in solu- 

 tion, but in tolerably strong concentration. 



"The cell sap consists of a solution made up of such 

 substances as sugars, salts and acids, as a result of which 

 the freezing point is soTuewliat lower than 32 deg. F. 

 The water in the iirofoplasm also contains certain sub- 

 stances in solution, so that its freezing point becomes the 

 same as that of the solution within the same cell. "Water 

 in a plant can therefore not be frozen before the temper- 

 at"re lias gone below the freezinsr point for the cell sap 

 anil, as explained above, the sfrovrjr'- the solution llir 

 mnrc' must the trmperatnre sink before freezivfj shall 

 .-lotei? pldee: A "ripe apple which is rich in sugar requires 



a lower temperature before freezing takes place than 

 does one which is immature and poor in sugar." In 

 a number of apples which were examined by Hedlund 

 after the warm sunny summer of 1901 he found that 

 their freezing point was about — 3 deg. (' (26.6 deg. 

 F. ) The osmotic pressure of the solution within these 

 apples consisted consequently of about thirty-six at- 

 mospheres. It is pointed out further that the soluble 

 substances within the cells define a certain limit for 

 freezing and consequently for the re=arrangement of the 

 small plasmatic particles. "The ice which is formed 

 between the cells consist of pure water. In the same 

 measure as this is drawn out of the cells for the forma- 

 tion of ice the concentration of the remaining liquids 

 becomes increased. When the cell sap has become so 

 concentrated that its freezing point sinks to that of the 

 surroTuiding temperature, the freezing is delayed and 

 the protoplasm is protected again.st a further shifting of 

 its small particles. If within the cells there are found 

 substances stored up which are not soluble in water such 

 as starch or oil, then is the concentration obviously in- 

 creased much more quickly during freezing, which latter 

 consequently takes place at a lower temperature than 

 when the same cells are poor in such stored-up matter." 



"Assuming that a cell contains insoluble constituents 

 to five-sixths of its inner volume, and that this on freez- 

 ing become decreased bj^ one-twelfth, there is produced 

 as a result a doubling in the concentration in the cell's 

 sap, other things being equal. Had the constituents of 

 the same cell consisted only of one-third of insoluble 

 substances and the freezing point, before freezing, had 

 been the same, then had the cell sap not reached that 

 concentration which in the foregoing case had prevented 

 continued freezing before the volume had been de- 

 creased by one third, that is after the volume had been 

 decreased four times as much as in the former case. The 

 storuig up of soluble as well as insoluble substances in 

 the cells during the summer is consequentUj an active 

 means of protecting the protoplasm against damage by 

 freezing." This protection against frost damage can be 

 very materially aided by the addition of certain chem- 

 ical constituents to the stored-up material, a fact which 

 suggests the careful feeding of ]3lants even to the extent 

 of supplying this food through the medium of commer- 

 cial fertilizers. A few of the conditions which are ne- 

 cessarj' in order that trees and bushes may possess the 

 highest possible degree of frost hardiness are, according 

 to Hedlund, as follows: "Protoplasm shall have finish- 

 ed its activity in good time iu the autunni and shall have 

 assumed such a (luality that it may resist the re-arrange- 

 ment of its small particles. The cells shall be rich in 

 stored-up materials, both soluble and insoluble. The 

 shoots should also be furnished with a strong layer of 

 bark, a condition which in comparison with the two 

 foregoing is of subordinate importance. The physiolo- 

 gical essentials for good winter hardiness in the case of 

 fruit trees are essentially the same as for the abundant 

 production of flowers. The situation in which the plant 

 is placed shall be sunny and warm, so that an abundance 

 of carbohydrates can be prepared. Since carbonic acid 

 assimilation is favoured by a relatively moist atmos- 

 phere in that the stomata under such conditions are 

 more likely to remain open, trees and bushes are able to 

 withstand more severe frost in a coast climate. 



"Soil must not become so saturated with water that 

 the roots are prevented from taking up sufficient plant 

 food and even water, the latter boins necessary to take 

 the place of that which passes off from the leaf by trans 

 piration, because inider these conditions carbonic acid 



