70 THE STUDY OF LIVING CELLS. 



PREPARATION SECOND: For young POLLEN-GRAINS. (Fig. 9.) Take a 

 staminate flower somewhat older than the first. (The exact stage will 

 have to be obtained possibly after trying several buds.) Section 

 and prepare as before. Stain with iodine, letting it run under the 

 cover one-third of its diameter. Focus on that region bordering on 

 the stained and unstained portions. 



OBSERVE: 1. The mother-cells (of pollen grains), floating free 

 in the water, and the exceeding thinness of the walls. 



2. The contents of the mother-cells four small -'pollen 

 grains" ; or if only three appear focus carefully to ascertain the 

 presence of a possible fourth. 



3. Form of pollens ; their nucleus and protoplasmic contents. 



4. The readiness with which the protoplasm of the pollen 

 becomes stained, even when the water medium appears scarcely 

 tinged. 



5. Mother cell wall, almost colorless, although the iodine 

 must have passed through it. Why? 



6. Is the place between the mother-cell wall and the contained 

 pollens more tinged than the water medium? 



Figures of developing pollen grains, Goebel, p. 362; Stras- 

 burger, p. 313 ; Sachs' Physiology, pp. 99, 100. 



Draw one or two mother-cells with contained pollens. 



PREPARATION THIRD. For MATURE POLLEN GRAINS. From the 

 mature anther of an open flower jar' out the pollen, letting it fall on 

 a dry slide. Examine carefully with a microscope, and then apply 

 water to the side of the cover-glass. 



OBSERVE: 1. Appearance of the pollen grains when on the 

 dry slide. 



2. Change of form when the water is applied; the cause? 



3. The wall, its relative thickness as compared with that of 

 the mother cells. 



Measure a large and small grain, the longer and shorter axis. 

 Draw a grain in the dry condition, and one in the moist. Sachs' 

 Botany, p. 15; Bessey, p. 23; Gray's Structural Boi, pp. 256-257; 

 Bot. Centralbl., Beih., 1893, pp. 206-17, 321 54, 401-36. 



Illustration Second: POLLEN-GRAINS from the Order Mal- 

 vaceae, (either Hibiscus or Abutilon.) 



