THE FOOD OF THE PLANT 5 



To insert the plant it is well to cut a wedge-shaped 

 piece out of the cork, fit the stem into the gap, cut 

 off the angular end of the wedge and replace the 

 remainder (Fig. 1). 



The glass vessel is then filled with water and the 

 cork inserted. 



After this the thistle-funnel also is filled with water, 

 and the tap is then carefully turned until water fills 

 the whole apparatus, including the bent tube. Great 

 care must be taken that no air is left in the apparatus. 

 The expulsion of air is facilitated if the short arm of 

 the narrow glass-tubing does not project beyond the 

 bottom of the cork. 



All connections must now be made air-tight. To 

 this end a little paraffin-wax is melted in a porcelain 

 evaporating dish. The paraffin should be allowed to 

 cool until it is just settmg, then it must be put over 

 all the fittings of the apparatus and worked in well 

 with the fingers. This method will be found cleaner 

 and more effective than the pouring of melted paraffin 

 over the joins. It will also prevent possible injury to 

 the plant from the use of paraffin that is too hot. The 

 beginner will often find it difficult to get a piece of 

 apparatus air-tight ; if all the corks are soaked for a 

 little while in melted paraffin before being used this 

 difficulty is greatly lessened. Plasticine, instead of or 

 in addition to paraffin, can often be used with advantage 

 in making difficult fittings air-tight. 



Observations. — Mark the time taken for the water 

 to be absorbed through a measured portion of the tube. 

 Then refill the tube by means of the tap. Take at 

 least two more readings and record the time taken in 

 each case. If the observer wishes, the actual volume 

 of water absorbed in a given time can be calculated 

 from the formula 7rr% (where 7r = ^, r= radius of tube, 

 A, = length of tube). 



It is more important, however, to compare the rates 

 of absorption under different conditions. Thus : 



1. Remove the apparatus to the coldest place 



