174 PRACTICAL COURSE IN BOTANY 
8. Is the practice of lopping and pruning very closely, as in the process 
called “‘pollarding,” beneficial to a tree under ordinary conditions? (186, 
189; Exp. 63.) 
9. Name some plants of your neighborhood that grow well in the shade. 
10. Compare in this respect Bermuda grass and Kentucky blue grass ; 
cotton and maize; horse nettle (Solanum Carolinense) and dandelion ; 
beech, oak, red maple, dogwood, pine, cedar, holly, magnolia, etc. 
11. Name all the aromatic leaves you can think of ; all that are used as 
food, beverages, drugs, and dyes. 
12. What is the use of aromatic and medicinal leaves to the plant itself ? 
(Suggestion: Why does the housewife put lavender or tobacco leaves in 
her woolen chest ?) 
13. Which would be richer in nourishment, hay cut in the evening or 
in the morning, and why? (54, 186; Exp. 70.) 
14. Mention three important sanitary services that are rendered by a 
tree like that shown in plate 6 or 8. (180, 185, 189.) 
15. Name some of the plants employed in the manufacture of starch. 
VI. THE LEAF AN ORGAN OF RESPIRATION 
Marerrau. — A number of vigorous, freshly cut green leaves; a liter 
or two (one or two quarts) of expanding flower or leaf buds. 
Appliances. — Some wide-mouthed jars of one or two liters’ capacity ; 
two small open vials of limewater. 
EXPERIMENT 72. Do LEAVES GIVE OFF CARBON DIOXIDE? — Cover 
the bottoms of two wide-mouthed jars with water about two centimeters 
(1 inch) deep. Place in one a number of healthy green leaves with 
their stalks in the water, and insert among them a small open vial con- 
taining limewater. In the other jar place only a vial of limewater in the 
clear water at the bottom, this last being merely to make the conditions 
in both vessels the same. Seal both tight and keep together in the dark 
for about 48 hours, and then examine. In which jar does the lime- 
water indicate the greater accumulation of CO2? (It may show a slight 
milkiness in the other vessel due to gas derived from the inclosed air and 
water.) From this experiment, what process would you conclude has 
been going on among the leaves in jar No.1? (Exp. 25.) 
EXPERIMENT 73. Is THE EXHALATION OF CARBON DIOXIDE ACCOM- 
PANIED BY ANY OTHER CONCOMITANT OF RESPIRATION ?—In Exps. 24, 
25, it was shown that respiration is accompanied by heat; hence, if the 
production of carbon dioxide by the leaf is due to this cause, it should be 
attended by the evolution of heat. To find out whether this is the case, 
partly fill a glass jar of two liters’ capacity with unfolding leaf buds ar- 
