128 PRACTICAL BOTANY. 



will be found that the time of appearance of the pollen-tube will 

 vary in different cases ; also that to obtain good results solutions 

 of sugar of different strengths will have to be used. In most 

 cases a solution of 10 per cent, or less will be found suitable. 



Development of Anther and Pollen. 



If transverse sections be made from very young buds, and suc- 

 cessively from older ones up to the mature flower, the develop- 

 ment of the anther and of the pollen may be traced. 



The material should be preserved in absolute alcohol (or strong 

 methylated spirit), and the sections should be treated with half 

 glycerine, half alcohol ; this should be left exposed to the air in a 

 watch-glass, so that the alcohol may evaporate ; mount in pure 

 glycerine. 



(Anhydrous staining reagents may be employed.) 



By following this method, sections may be prepared 

 illustrating : 



1. The formation of the four masses of tissue in the anther 

 (two in each lobe), each of which subsequently becomes 

 differentiated into : 



(a) A peripheral coat of cells of the tapetum, which take no 

 direct part in the formation of the pollen, and 

 (6) A central mass of pollen-mother-cells. 



2. The division of each of the pollen-mother-cells into four 

 special-mother-cells, by the gradual ingrowth of the wall of 

 the mother-cell. 



3. The separation of the members of the tetrads thus formed, 

 and their subsequent development as pollen-grains. 



4. The gradual disorganisation of the tapetum. 



5. The development of the wall of the anther, as above 

 described, and breaking down of the septum between the pairs 

 of pollen-sacs. 



Compare similar preparations of the young anthers of Trades- 

 cantia, and note the division of the pollen-mother-cells, without 

 any gradual ingrowth cf the wall. 



Observe, as far as possible, the divisions of the nuclei of the 

 pollen-mother-cells first into two, then into four ; also the two 

 nuclei in the mature pollen-grain. 



