TRANSPIRATION. 209 



course affected by factors which bear upon the absorbing 

 roots. The chief of these are (1) the quantity of water 

 available ; (2) the temperature of the soil ; -(3) the 

 soluble substances present in the soil. In each of the 

 following experiments use the weighing method, with pot 

 plants in which pot and soil are covered e.g. with an 

 aluminium shell. 



(a) Determine the loss of weight by transpiration of 

 two similar plants, one of which (A) is supplied each day 

 with as much water as has been lost during the preceding 

 twenty-four hours, while the other (B) is left entirely 

 unwatered. 



(6) Put a thermometer in the soil with a pot plant. 

 For a day determine its transpiration loss under normal 

 conditions. Then immerse the pot in a vessel of chopped 

 ice, with a felt pad or other packing of non-conducting 

 material to prevent the ice from cooling the leaves. 

 Determine the loss of weight in three hours, after 

 removing the pot from the ice and wiping it dry. Leave 

 the plant for an hour to recover, then place it in a vessel 

 of water heated by a spirit-lamp or Bunsen until the soil 

 is at 35 C. ; keep it at this temperature for three hours, 

 and find the transpiration loss for that time. 



(c) Determine the daily loss of a pot plant for two 

 days, and then water the soil on three successive days with 

 1'5 per cent., 1 per cent., and 0'5 per cent, of potassium 

 nitrate, and observe the effect on the amount transpired 

 each day. 



272. Transpiration checked by Bloom, Cuticle, 

 and Cork. By simple weighing experiments we can 

 demonstrate the importance of these coverings in reducing 

 transpiration from leaves, etc. 



(a) Select three apples of about equal size, well covered 

 with waxy bloom. Rub one (J.) with a cloth dipped in 

 warm water, so as to remove the bloom (water at 35 C. 

 will not injure the cells) ; peel the second (B) ; and leave 

 the third (C) untouched. Weigh the three apples, place 

 p. B. 14 



