CHAPTER IV. — PRACTICAL EXERCISES. 263 



10. In the summer season, by searching among the pieces of moist tan- 

 bark about a tannery yard, specimens of yEthalium septicum, one of the Slime- 

 moulds, may usually be found. They form yellowish, gelatinous masses of 

 various shapes and sizes, sometimes as large as a pigeon's egg or larger. Having 

 found one of these plants, support the piece of bark to which it adheres in an 

 upright position under a bell-jar, with an end resting on a moistened sponge, 

 and expose the jar to diffused light in a window, in such a manner that the 

 plant will be on the illuminated side ; after a time it will be found that it has 

 moved around to the shaded side of the bark, showing that it is sensitive to 

 light. 



With care it may be made to creep upon a glass slide, and the pseudopodia 

 and streaming movements of the protoplasm may then be studied under a 

 compound microscope. 



If the mass be struck a sudden blow, as with the flat side of a knife-blade, 

 but not so hard as to crush or disorganize the protoplasm, it will be observed 

 to contract, and its amoeboid movements will cease for a time ; but if left to 

 itself for a while under favorable conditions, the movements will be resumed. 



It will not be difficult to arrange an experiment so as to send a weak current 

 of electricity through the mass after it has resumed its activity. One electrode 

 of the battery should be placed gently in contact with one side of the mass and 

 then the other should be brought into contact with the opposite side. The 

 moment the circuit is completed, sudden contraction will be observed to take 

 place as before. 



11. On the young tendril of a healthy vine of the Wild Cucumber (Echin- 

 ocystis lobata), place a piece of twine a few inches long, and allow it to remain 

 for a few hours and then observe the result. It will probably be found that 

 the tendril, in response to* the stimulus, has bent toward the string. Continue 

 the experiment, and observe and record the final result. The experiment may 

 easily be varied in such a manner as to ascertain how small a weight of string 

 will suffice to produce movement in the tendril. 



