1 82 THE TEACHING BOTANIST 



Other topics of interest and value on germination are : 



How the seed-coats are burst in different seeds. 



How the embryo breaks out of the ground. 



How the embryos fasten themselves to the ground to give 



a resistance to enable the hypocotyl to bore into the 



ground. 

 The behavior of the food substance in germination. 



Experiment No. i . This experiment is of the utmost impor- 

 tance, since it gives a logical understanding of the true nature of 

 geotropism, a typical form of irritability, and one of the easiest 

 to understand. If geotropism is once understood, it will make 

 all other forms of irritability easily comprehended. Irritabil- 

 ity in plants answers to sensation in animals, and a clear con- 

 ception of it is essential to the understanding of the most 

 important peculiarities of plant form, movements, and adapta- 

 tion of the individual to its environment. I believe that one 

 of the greatest advances that could be made toward placing 

 the teaching of Botany upon a truly scientific basis would be 

 through the introduction into it of a correct teaching of irrita- 

 bility. Of course the teacher must first be trained, or train 

 himself, in this vital subject. 



Experiment i can be performed very satisfactorily, as fol- 

 lows : Pin to each of two corks, five inches in extreme diameter 

 and one inch thickness, five or six soaked Horse Beans in as 

 different positions as possible, though alike on the two corks. 

 Slip the Beans out to the heads of the pins a half inch or more 

 from the corks. Place around, over, and under them clean, 

 moist, chopped Sphagnum moss, and then fit over the corks 

 thin crystallizing dishes (see Fig. 17), about two and a quarter 

 inches deep, and wide enough to just hold well on the bevelled 

 edges of the corks when these are pushed into them (i.e. four 



