THE ANGIOSPERMAE 



1181 



ditterent forms in the same flower is called heterostemony. From this 

 category should be excluded all cases of abortive or vestigial stamens, 

 whether transformed into staminodes, petals or other forms. The term 

 should apply only to those flowers with different forms of fully fertile 

 stamens. Thus delimited it is not a common phenomenon and is usually 

 associated with zygomorphy. A difl^erence of size alone is characteristic 

 ot the stamens of Cruciferae and Labiatae and is not infrequent in 

 Leguminosae and Scrophulariaceae. Cassia, a large genus of Leguminosae, 

 shows not only a difference of size, but also sometimes of form and 

 function among its stamens. The three uppermost are sterile and dwarf, 



Fig. 1 1 54. — Coryodaphnopsis tonkinensis. A, Floral diagram. B, 

 stamen of second whorl, face view. C, Stamen of outer whorl, 

 face view. D, Stamen of third whorl, abaxial view. E, Staminode 

 of inner whorl. {After Hooker: ' Icon. Plant.') 



the four lateral are longer and their pollen is eaten by insect visitors, while 

 the three lowest are large, functional in pollination and project from the 

 flower, sometimes to the right hand and sometimes to the left. In the 

 Scrophulariaceae, Verbascum also shows a qualitative heterostemony, three 

 stamens bearing hairs and two being glabrous. Commelina (Commeli- 

 naceae) has three posterior stamens with enlarged, yellow-coloured con- 

 nectives which form part of the attraction of the flower. They are fertile, 

 though with small pollen-sacs, and they are larger than the three anterior 

 stamens. The above are all variations between stamens of the same whorl, 

 but variation also occurs between stamens at different levels on the re- 

 ceptacle, as in many Lauraceae, where three distinct types of stamen may 



