452 How Aimnals and Plants Reprodnce unit viii 



5. How may pollen tubes be made to grow? Shake pollen from ripe 

 anthers into a 10 per cent sugar solution. (If the pollen fails to produce 

 tubes, vary the concentration of sugar.) Set aside and examine after a few- 

 hours. Draw the pollen tubes in various stages of development. Stain with 

 iodine solution and look for nuclei. How many do you find? 



6. If a tulip blossom is available, transfer some ripe pollen with a tooth- 

 pick to the stigma of the pistil. (The stigma must be well expanded.) 

 After three or four hours, cut a small piece from the stigma, crush it on 

 a slide, mount it in water and examine it under low power. Look for pol- 

 len grains and note the tubes. Look for nuclei. 



7. You have already studied the bean seed. What is found inside the 

 seed coats? Of what three parts does the embryo consist? Does food seem 

 to be stored in this embryo? Where? Now cut a kernel of corn length- 

 wise. The kernel is a small fruit which is completely filled with a single 

 seed. Lay the cut surface into a dish of iodine and examine. What do you 

 know about the portion that turns blue? This is food material or endo- 

 sperm. Now draw what you see. What proportion of this seed is embryo, 

 what proportion is endosperm? 



8. To what extent is a pea or bean seedling dependent on the food 

 stored in its cotyledons? Carefully cut away the cotyledons from several 

 seeds which have begun to sprout. Give them favorable conditions for 

 growth (moisture and warmth). Leave the cotyledons on several seeds 

 and keep them with the others. Observe closely and record. What con- 

 clusions do you draw? Cut away one cotyledon and repeat the experi- 

 ment. Does this make you more sure of your conclusions? Why or why 

 not? 



9. What do you learn from the study of the pea pod? Carefully examine 

 the outside of a pea pod close to the stem. Where have you seen these 

 parts before? If you have a blossom of the garden or sweet pea take out 

 the pistil. Lay it next to the pea fruit. What resemblances do you find? 

 From which part of the flower did the pea pod develop? Open the pod 

 carefully so that the "peas" remain attached. If the pea pod is a fruit what 

 are the "peas"? What were the "peas" when they were young? Does the 

 pod contain any undeveloped seeds? Explain. The region of the fruit to 

 which the seeds are attached is the placenta. Why must the ovules (and 

 young seeds) be attached to the ovary? The pea pod illustrates the origin 

 of a fruit. What can you conclude about fruits in general? 



10. Study the following fruits and seeds and as many more as possible: 

 Linden, maple, elm, burdock, cocklcbur, beggar's tick, dandelion, thistle, 

 milkweed, cotton, strawberry, raspberry. VVhich of these fruits or seeds 

 have structures which result in their bein<j scattered by the wind? Which 

 would be carried the greatest distance? Why? Examine the burdock, 

 cocklebur, and beggar's tick. How are they likely to be dispersed? 



1 1. Asexual reproduction in ferns. Using a hand lens, examine the lower 

 side of a fern frond (leaf) whicli has formed spores. You can see masses 



