THE WHITE LILY 199 



there are no characteristic differences between the two 

 Classes here. Their similarity is equally marked, 

 whether we consider the general plan of the flower, 

 the structure of its several organs, or the minute 

 details of their development. Apart from one or two 

 trivial and not very constant differences, we may say 

 that every detail in the development of the perianth, 

 of the stamens, of their pollen-sacs and pollen, of the 

 pistil, the ovules, the embryo-sac and the endosperm, 

 as well as the process of fertilisation, shows the most 

 minute correspondence in both Classes. In fact, so 

 close is the agreement in all important characters, that 

 if we want to find a ready means of distinguishing 

 these Classes by their flowers, we have to fall back on 

 arithmetic, and make what use we can of the rule that 

 in Monocotyledons the parts of the flower are usually 

 in threes, and in Dicotyledons in fours or fives ! 



On the whole, we may say that the points of agree- 

 ment between our first two types much outweigh the 

 points of difference. 



The classes Dicotyledons and Monocotyledons to- 

 gether constitute the sub-kingdom Angiosperms, char- 

 acterised by the fact that the ovules are contained 

 within a closed ovary, and that consequently fertilis- 

 ation has to take place through the intervention of a 

 stigma. 



