228 THE TEACHING BOTANIST 



Can pressure be exerted in this process of absorp- 

 tion ? 



Answer by Experiment 10. 



51. Prepare a synoptical essay (of not over three hun- 

 dred words) on the Cellular Anatomy of the 

 Higher Plant. 



Materials. - - Roots are much alike in their anatomy, and 

 almost any will do for the anatomy of the shaft called for in 

 Exercise 48 ; the students' own scalpel sections will show rela- 

 tive development of the principal tissues. Splendid tips and 

 root hairs may be obtained thus : take a small, very porous 

 flower-pot saucer and place in it seeds of Radishes or 

 Mustards, soaked a few hours ; cover with another saucer 

 and set it in a dish of water deep enough to keep the seed 

 saucer always wet. In three days the roots and hairs will 

 be perfectly developed. As many saucers and as few students 

 as possible to each is best. It is also well to have a few of 

 the same kinds of seeds sown at the same time in earth, to 

 show how the earth affects the growth of the hairs in com- 

 parison with their free and symmetrical development in the 

 saucer. The hairs in the saucers wilt very quickly when 

 exposed to the air. 



The Mustard shows the tip and cap, with the radiating 

 lines of growth, even without any special treatment and with a 

 simple lens, but the potash makes them much plainer. 



Pedagogics. - - An exercise excellent for observation, and 

 particularly valuable for its introduction to the very important 

 subject of absorption of liquids. Under Exercise 49 they 

 should not fail to make out that the zone of hairs advances 

 not bodily, but by growing in front and dying behind. Here 



