EXERCISE 118 



Seeds develop from ovules, but only, as a rule, after protoplasm from the pollen reaches and fuses 

 with protoplasm inside the ovule. 



Problem. How does the protoplasm from the pollen reach the inside of the ovule ? 



What to use. Some live flowers ; slides ; dilute sirup (sugar in water, about three per cent) ; moist 

 chamber ; section cutter or razor ; prepared sections of ovules. 



What to do. 1. Get some pollen from the anthers of the flower to 'sprout in a drop of sirup on a 

 glass slide in a moist chamber (see Exercise 115) ; examine with the microscope. 



NOTE. The nucleus near the end of the pollen tube is the male, or sperm, nucleus, which is to unite with protoplasm 

 in the ovule. 



2. Examine the surface of the stigma to see (a) how pollen grains can find lodgment on it, and 

 (b) what would make pollen grains sprout there, forming pollen tubes. 



NOTE. The style is usually either hollow through the middle or made up of loose tissue through which a pollen tube 

 readily grows. 



3. Examine several ovules with low power of the microscope, to find the micropyle (see Exer- 

 cise 30) through which the pollen tube may enter the ovule. 



4. Examine sections of ovule and note the large cell on the inside the embryo sac, inside of which 

 the new plant, or embryo, is to develop. 



NOTE. The original nucleus of the embryo sac divides several times. One of the resulting nuclei is the female, or 

 egg, nucleus, and unites with the sperm from the pollen tube. 



Record. Draw and describe the structures studied. 



Questions. 1. How does the protoplasm of the pollen spore reach the ovule? 



2. How does the sperm from the pollen tube get to the embryo sac ? 



3. What is likely to become of the ovule as the embryo ripens ? 



4. How is the developing embryo nourished ? 



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