156 



1920, by Sprague in 1923, by Hutchinson in 1926 and by Zim- 

 mermann in 1930. A very brief outline follows: 



Ovules and Seeds 



1. Ovules many— >few 



2. Embryo straight^curved 



3. Endosperm present— ^absent 



4. Seedcoats 2— >1 



The number of ovules developing into seeds decreases in the 

 higher flowering plants. We see a similar evolution in the animal 

 world. For example, in fishes thousands or even millions of eggs 

 are laid. In mammals, only a few young are born, but these are 

 given better care. Many plants with a curved embryo grow in 

 dry climates where quick germination is important. In the case 

 of the Centrospermae a curved embryo is nearly universal; an 

 exception is Dianthus and related genera, with embryo nearly 

 straight. In the Engler system these genera come at the end of 

 Centrospermae. Should they be the beginning and thus connect 

 with Frankenia? 



Carpels 



1. Carpels many— >few 



2. Separate— ^partly united— ^wholly united 



3. Ovary superior— *half inferior— >wholly inferior 



4. Placentation parietal 



— >axile 



United carpels, an inferior ovary, and axile placentation are 

 all tendencies in the same direction, namely for better protec- 

 tion of the seed. Another specialized character is partly sterile 

 carpels. The absence or near absence of style and stigma must 

 be considered as primitive. Basal placentation may perhaps be 

 primitive in some cases and derived in others. 



Stamens 



1. Stamens numerous— >2 whorls— >1 whorl 



2. Free— ^more or less united 



3. From receptacle— >from petals 



4. Filaments broad— ^filiform 



Stamens few is a character of the advanced flowers. With 

 improved methods of pollination, less pollen is needed. Lin- 



