42 PHYSIOLOGICAL PROCESSES IN PLANTS 



Observation. Find any sproutlike tubes (pollen tubes) ex- 

 tending from the pollen grains. Describe them, or sketch a 

 few. 



Conclusions. 1. Are the stigmas in a blossom in such a 

 position that pollen might commonly reach them ? Explain. 



2. The sugar solution served as food for the growth of the 

 pollen tube. Can you see any reason for there being a similar 

 solution on the stigma? 



Note. The pollen tube is long and threadlike, and carries 

 in its growing end a very important structure (sperm cell). 

 (See Figures and Charts for further explanation.) 



c. The Pistil 



Materials. Pistils of such flowers as lily or tulip, some cut 

 lengthwise and some cut crosswise. Chart or text Figures. 



Observations. 1. Find a number of rounded bodies (ovules') 

 in the ovary. Describe one. 



2. Are the ovules few or abundant ? 



Note. The ovules become seeds if the sperm cell in the tip 

 of the pollen sprout ever succeeds in reaching a somewhat 

 similar cell (egg) located in the ovule. The pollen grain sprouts 

 in the sweet food on the stigma, and sends' the sprout down 

 through the style until finally the two cells the sperm cell 

 and the egg cell unite to form a single cell. See Figure 85. 

 The egg is now said to be fertilized, and the process is known as 

 fertilization. The fertilized egg now develops a minute struc- 

 ture called the embryo, and the ovule is now a seed. The 

 embryo of the seed will develop into the future plant when 

 the conditions needed are present. 



We now see that only pollen and eggs are necessary for the 

 formation of seeds, so the anthers and pistils are known as 

 the necessary or essential organs. 



