LABORATORY AND FIELD WORK 421 



to point the way to the places where nectar is produced ; peculiar 

 shapes of flowers which adapt them to pollination by particular 

 insects ; structures which keep out some insects. Of what ad- 

 vantage is each of -these adaptations to the plant? 



6. If possible, study some of the common wild violets in bloom. 

 Notice the showy flowers, and then look for other much less con- 

 spicuous flowers that never open. (Not all species of violets have 

 these inconspicuous flowers.) What parts do the flowers of the 

 latter sort have? In what way do they differ from the showy 

 flowers? Of what use to the plant are the inconspicuous flowers? 



Chapter XVIII 



1. Obtain such common fruits as are available. Determine 

 from what structure present in the flower each part of the fruit 

 has been developed. What changes has each structure undergone ? 



2. Note the number of seeds present in each fruit. How are 

 the seeds protected? 



3. Collect the fruits of several of our common weeds. Do you 

 find any special means in each case for the scattering of the fruits 

 or seeds ? , 



4. Make a hst of common seeds with, and of those without, 

 endosperm. 



5. Soak the seeds of several common plants in cold water for 

 twenty-four hours ; place some of each sort under different condi- 

 tions of temperature, keeping them between pieces of moist filter 

 paper or blotting paper. Note the percentage of germination in 

 each case. What differences do you find between different kinds 

 of seeds in their power of germination? What influence does 

 temperature have upon germihation ? 



6. Germinate soaked seeds in darkness and in light. Which is 

 the more favorable for germination? Are all seeds alike in this 

 respect ? 



7. Place some soaked seeds in a bottle filled with water which 

 has been boiled to drive out the air. Seal the bottle or cover the 

 water with a layer of oil and observe from day to day. Do the 

 seeds germinate? Explain. 



8. Sprout seeds of corn, peas, and beans. When the stems are 

 a half-inch long, remove one or both cotyledons of the beans and 



