342 



PERSONAL AND CIVIC HYGIENE 



2. Study Figure 86. Note that the end of the pollen tube containing 

 the sperm cell is about to unite with the egg. 



FIG. 86. Showing beginning stage of fu- 

 sion of germ cells in cotton plant. 

 (After Duggar.) P, pollen tube passing 

 through the micropyle, and carrying a 

 single sperm cell. E, egg. 



Note. The sperm cell is thought to 

 furnish the egg cell with a renewal of 

 vigor, so that it will now actively de- 

 velop to a mature plant. Otherwise it 

 would stop, after reaching the period of 

 growth represented by its condition in 

 the ovule before fertilization. 



b. Protozoa 



Considerations. 1. What is the 

 simplest method of reproduction in such a 

 simple-celled animal as a paramcecium ? 

 2. Will this method suffice for any 

 length of time ? 



3. What must happen to prevent the species from dying out? Note. 

 Conjugation is a term which may be used to denote either a temporary 

 or permanent fusion with another individual. 



