GERMINATION, GROWTH, TISSUE TENSION. 



147 



(6) Another method is to use Wheat grains, and grow 

 them with the roots in water. From some Wheat count 

 out thirty-six good sound grains, and divide them into 

 batches of a dozen each ; see that the weight of each batch 

 is as nearly as possible the 

 same. Dry one batch (A) 

 and record the dry weight. 

 Tie a piece of muslin over 

 a tumbler or bowl filled 

 with water, and put a batch 

 (B) of seeds on the surface 

 of the muslin, which should 

 be kept wet. Another plan 

 is to use a piece of flannel, 

 stab twelve holes in it, and 

 in each hole place a seed. 

 Keep the tumbler in a 

 warm, dark place, and re- 

 new the water every second 

 or third day. Plant the 

 third batch (0) as in (B) 

 and keep both at about 

 the same temperature, but 

 when the young shoots ap- 

 pear expose (0) to the 

 light. When the shoots 

 have grown several inches, 

 carefully remove the seedlings from (B) and (0), noting 

 the difference in colour between the two sets. Dry them 

 thoroughly, without charring even the finest rootlet, and 

 then weigh each lot and compare the weights of (A), (B), 

 and (0). 



189. Growth in Distilled Water. We shall see later 

 that green plants get their food from the air and the soil. 

 The young plant in a seed has a store of food for its early 

 growth, a store which is sometimes very scanty and some- 

 times (as in Pea and Bean) very abundant or even extrava- 

 gant. Tap-water and rain-water are not pure, but contain 

 dissolved substances, while soil-water and river-water are 



1234 

 Weeks 



Fig. 36. Chart on which to plot the 

 Curves of Height and Weight. 



