200 BOTANY FOR BEGINNERS CHAP. 



EXPT. 1 80. Cut transverse sections of the young flower bud of the 

 Wallflower. Mount the thinnest in water and examine with a low 

 power. Neglecting the other parts of the flower, look for an anther. 

 Note 



(i) A single layer of cells, the epidermis, the outer walls of which 

 possess a well-developed cuticle. 



(ii) The fibrous layer, which is several layers of cells in thickness and 

 appears striated. 



(iii) The tapetum layer. This is represented by a layer of cells in all 

 stages of disorganisation. 



(iv) The four pollen sacs. 



(v) The pollen grains. Some are in the pollen sacs, others in the 

 water. 



EXPT. 181. Transverse sections of a ripe anther of the Wallflower 

 should be made for comparison. To do this it is necessary to harden 

 in alcohol for a few days. Select the thinnest and mount in glycerine. 

 Note 



(i) The layers are the same, but better developed. 



(ii) There are only two pollen sacs. 



(iii) The pollen grains are ripe. 



Examine a pollen grain with a high power. Note 



(iv) The thin places in the wall through which the intine grows to 

 form the pollen tube. 



(v) The nuclei, the largest^ is the vegetative one, and the two smaller 

 ones are the generative ones. These will be seen with difficulty. 



EXPT. 182. Mount in water and examine the pollen grains of the 

 following flowers as they appear Rock Cress, Sunflower, Hyacinth, 

 Apple, Deadnettle, &c. Note 



(i) Their shape and external markings. 



(ii) The thin places in their walls. 



(iii) Their comparative sizes. 



EXPT. 183. Cut a piece of cardboard the size of a microscopic slip, 

 and out of the centre remove a circular piece the size of a cover-glass. 

 Fix the cardboard to the glass slip with a thin layer of Canada balsam 

 and dry ; place a drop of a six per cent, solution of sugar in the cell 

 you have formed in the cardboard. Mount a few pollen grains from 

 the Wallflower in the sugar solution, and cover with a cover-glass. 

 Examine with the high power of microscope. Note 



(i) The thin places in the wall of the grains. 



Damp the cardboard and put in a dark warm place for a few hours. 

 Note 



(ii) Many of the grains have sent out pollen tubes filled with granular 

 protoplasm. 



(iii) One or more nuclei may be detected in the pollen tube. 



How the Pollen is liberated from the Anther. When 

 the anther is ripe, the pollen sacs open so as to set the pollen 

 grains at liberty, The anther lobes may open by one split 



