16 Selim Lemström. 



To what degree the température will fall dnring a very strong night-frost 

 in summer and autumn bas not been witb certainty determined, but we are 

 very likely near tbe truth if we assume tbat the température of vegetables 

 near the ground may fall to —6" during tbe summer until the 10 September. 



In tbis place we must l'emember that tbe upper parts of vegetables, at 

 least those wbich are turned upwards, probably radiate more lieat and hence 

 sufïer a greatei' fall of température, whicli still dépend on their beight. 



II. 



TO WHAT TEMPERATURE CAN PLANTS BE EXPOSEI) 

 WITHOUT DAMAGE? 



Thougb expérience in tbis matter is not extended enougli to give a sure 

 answer to tbis question, some conclusions of importance migbt still be derived 

 from it. 



All plants are not equally affected by a low temperatui'e. Among our 

 common vegetables the potato is one of the most sensible. Far less susceptible 

 are tbe cereals as oats, corn, rye, wheat, more sensitive pea, vetcb etc. at least 

 during the first stages of growth. 



As a general rule it can be stated througb expérience : that none of these 

 plants will be damaged by the simple forming of ice or rime around it, unless 

 the dew-point lies under zéro. 



Concerning tbe rye it is commonly known that the ears during the time 

 when tbey are most sensitive, i. e. the flowering time, can be coated över witb 

 ice without being damaged. 



I bave observed tbis fact many times but especially in a tield of rye in 

 the ears of whicb parts of the bloom were fully developed. The température 

 of the surrounding was already at 1. a. m. 2°,o and tbe field continued to cool 

 down for anotber 1 i hour, after whicb time the first sun-beams feil upon it 

 without damaging one single ear. During the autumn 1892 (Sept. 24), I 

 observed potato plants at a temperatui'e of - l^o fully covered with ice without 

 being damaged. 



The circumstances at tbe forming of ice are liere of importance. 



Tbey are principally: the rekasim) of the melting-heat (80 Cal. for every 

 kilogramm water) and the growth of volume. The heat released by the freez- 

 ing is partly utilized l)y the plant and the ice formed by tbe dew is a good 



