THE ANGIOSPERMAE 



1 195 



Barley in 1947. The condition is called " Yawning ", because of the gaping 

 appearance of the affected spikelets. It is unsafe to read too much meaning 

 into such monstrosities but they do emphasize the morphological unity of 

 the floral organs. 



Fig. 1 170. — Podophyllum peltatum. Carpelloid stamens. A, Vertical section showing 

 stigmatic surface, attached ovule and normal pollen-sac. B, Stamen with stigmatic 

 fringe and ovules. C, Stamen with stigmatic hood surrounding o\'ules and an open 

 cavity. D, Mature normal embryo-sac from a staminal ovule. {After Saiiyer.) 



The anatomical structure of the normal stamen filament is very simple. 

 There is a single, median, collateral or concentric vascular bundle and a 

 parenchymatous cortex surrounded by an epidermis containing stomata, 

 though no chlorophyll exists in the tissues. Where the filament bears a 

 conspicuous appendage, such as the hood in Asclepias, the bundle may form 

 a loop into it, returning on its course to pass up into the anther. Stamen 

 appendages of stipular nature on the other hand are supplied by a branch 

 from the main bundle, if they have any vasculation at all. 



Concrescent stamens retain distinct bundles in each stamen-unit, but 

 branched stamens have a common bundle at the base, which divides to send 

 a branch into each segment. When stamens are adherent to petals or sepals 

 the stamen bundle may remain separate or it may be united, in its lower 



