648 LABORATORY EXERCISES 



in distilled water containing the spores of the fungus. The seeds should be pre- 

 viously sterilized, as described above, and the suspension of spores made as above 

 directed. Healthy plants should be raised from uninoculated seeds as checks on 

 the progress of the disease in inoculated plants. 



Inoculate sweet pea plants with Sclerotinia libertiana by introducing pieces of 

 the fungus into pots in which sweet peas are growing. Have a potted plant as a 

 check and cover both plants with a bell jar in order to imitate the moisture condi- 

 tions of the greenhouse. After four to si.x days, wilting of the inoculated plants 

 will be noted, while the check remains in a perfectly healthy state. 



LESSON 35 



Experiments with Artificial Wounding of Plants. 



1. Take any herbaceous plant such as hyacinth, snowflake, daffodil, and by 

 means of a pair of scissors make a short cut into the tissues of the leaves of these 

 plants, into enough of leaves, so that a serial study can be made of the formation 

 of healing tissue. Pieces of the leaf are taken from time to time and sectioned by 

 any of the methods described in Lesson 42. 



2. Take any living shrub or tree and make the following cuts: 



(a) With a knife cut out a thin longitudinal piece of bark down to the cambium. 

 {b) Make an irregular tear in the bark by removing a small piece down to the 

 wood. 



(c) Cut out a ring of bark half way around the stem. 



(d) Make incisions into a pine tree and by means of sections study the flow of 

 resin and the healing operation. 



(p) Make incisions into the ordinary rubber plant Ficus elastica, and study 

 with sections the effect of the injury on the cells affected. 



(/) Make incisions into any of the woody euphorbiaceous plants of the greenhouse 

 and study the injuries produced in a similar analytic manner. 



3. Cut out larger pieces of bark from deciduous trees and shrubs and by sections 

 study the formation of cells. By several trips to the fields much of the material 

 illustrating the healing of wounds can be obtained for the making of sections and in 

 all stages of development without waiting for the slow development of new tissue in 

 the experimental plants. Cut with sliding microtome. 



Note the formation of tyloses in many of the woody stems studied. Linden is an 

 especially good tree to show their formation. 



Study callus formation of various cuttings, for e.xample, Ficus, Geranium, Ostrya, 

 Populus, Quercus and Ulrnus. Place the ends of these cuttings in different media, 

 as follows: 



1. One end in water, the other end in dry air. 



2. One end in water, the other end in moist air. 



3. Both ends in moist air. 



4. Both ends in water. 



5. One end in moist air, the other in dry air. 



6. One end in water, the other in moist sand. 



