50 THE BIOLOGY OF THE CELL 



determine the use of any of these ? What means 

 of protection from being dried, eaten by insects, 

 attacked by parasitic fungi, etc., do the pollen 

 grains exhibit ? Examine the stigmas or tips of 

 the pistils of the flowers of several different kinds 

 of plants, and note the presence of pollen grains 

 in some if not in all cases. Do you find in any 

 case that the pollen grain has means of its own 

 for getting from the anther to the stigma — i. e., 

 has it any organs of motion ? If not, how does 

 it make Its way from one part of the flower to 

 the other ? Examine the grains for the presence 

 of protoplasm, nucleus, chromatophores, oil drops, 

 etc., using reagents if needed. 

 Draw several specimens to show the variations in 

 shape, size, and markings. 



PHTSIOLOGT 



a. Germination. — Make a dilute syrup or nectar by 

 placing seven or eight crystals of "granulated" 

 sugar in a drop of water on the slide. "When 

 they have dissolved, dust into the drop a few 

 grains of pollen from some of the flowers named 

 above, preferably the Sweet-pea. Let the grains 

 remain in the syrup for several hours, examining 

 from time to time to study the formation of the 

 pollen tube. Note its size and rate of growth in 

 different grains. Compare with the germination 

 of the spores studied in Example 3, and note all 

 of the resemblances and differences that you can 

 discover. Much more successful cultivations may 

 be made in a hanging drop in a moist chamber. 

 Pollen grains which have germinated under natu- 



