204 PRACTICAL BOTANY 



In sections of anthers of medium age and successively of later 

 development the following points are to be observed 



1. 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. 



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

 and their subsequent development as pollen-grains. 



3. The gradual disorganization of the tapetum. 



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

 described, the most marked constituent of it being the fibrous 

 layer. 



Compare similar preparations of the young anthers of Trades- 

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

 any gradual ingrowth of 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 : in order to obtain good results, 

 it will be well .to stain with haematoxylin, methyl-green, or some 

 other reagent which colours the nuclei. 



CARPEL AND OVULES. 



IV. The following preparations must be made from 

 materials hardened in absolute alcohol, or methylated 

 spirit. From an open bud of Caltha palustris which has 

 been thus treated, strip off the outer organs, and cut 

 a large number of transverse sections of the carpels. 

 Treat the sections with one-half pure glycerine, one- 

 half alcohol, in a watch-glass, and let the alcohol 

 evaporate gradually : pick out those sections which 

 appear to have fairly traversed one or more of the 

 ovules, and mount them in pure glycerine. 



Strasburger recommends that in the preparation of such objects 

 the transfer to pure glycerine should be made before the sections 

 are cut. 



