71 THE STUDY OF LIVING CELLS. 



PREPARATION FIRST. This should be similar to that of pre- 

 paration third under Begonia. 



OBSERVE: I. The short processes, sometimes lobed, covering 

 the face of the grain. 



II. If the water causes the grain to swell. 



III. The size, measuring with the micrometer. 

 PREPARATION SECOND: Culture of POLLEN GRAIN and the study 



of germinating POLLEN TUBES, Tradescantia or Begonia. 



Sterilize a slide, cover-glass, and ring, for making a cell. This 

 can be done by heating them for some time in an oven at about 

 128 C., or quicker, by passing them slowly through the flame of an 

 alcohol lamp. Make a 10 per cent, sugar solution and boil it ten 

 minutes. Then with a platinum wire, cooled after passing through 

 an alcohol flame, place a small drop of sugar solution in the center 

 of the sterilized cover-glass. Sprinkle on this a very few pollen 

 grains and invert over the ring, which is placed in the center of the 

 slide and held in position by a drop of water at its lower edge. 

 The culture will then have the arrangement shown in Fig. 8. Re- 

 move the slide to a moist chamber and allow it to remain in a warm 

 place for a few hours. 



Fig. 8. Showing the method of cultivating pollen grains in \\ hanging drop. 

 A. Glass slide. B. Glass ring. C. Hanging drop containing pollen grains. D. 



Cover-glass. 



Examine the pollen grains after a few hours with a 1-6 objec- 

 tive taking care not to break the cover-glass by forcing the lens 

 against it. 



OBSERVE: 1. The outer and inner coat of the grain; the for- 

 mer is called the extine, the latter the intine. 



2. Pollen tubes of varying lengths projecting from the several 

 grains, usually but one tube from each grain (there may, however, 

 be several). 



3. The thin icall of the pollen tube continuous with the intine, 

 and the extine ruptured by the germination. 



4. The granular contents of the pollen tube consisting of 

 protoplasm and starch, together with the nucleus of the grain, on 



