114 MORPHOLOGY OF THE ANGIOSPERMS 



Upper part of the filament. These anthers, now inverted, could well be 

 called adnate but apparently have not been so described. Where the 

 filament is "attached" on the broad side of the anther, the anther is 

 dorsifixcd. This is a poor distinction, because the point of attachment 

 is difficult to determine when the connective is greatly reduced. Dorsi- 

 fixed anthers may stand at any angle to the filament. Where the tip of 

 the filament is delicate and the anther is free to turn at the point of 

 attachment, die anther is versatile. The place of attachment of the 

 versatile anther varies from the base to the top of the anther. These 

 anthers are dorsifixed and, if attached near the base, may also appear 

 basifixed. Distinguishing between versatile types has caused confusion, 

 as in description of grass flowers. Versatile anthers may be associated 

 with either insect or wind pollination, but are often considered to 

 characterize anemophilous plants. Basifixed is obviously a primitive 

 type; dorsifixed and versatile, advanced types. 



The Sporangia 



Number of Sporangia. Characteristically, the sporangium number is 

 four, with arrangement in two pairs, one pair on each lateral half of 

 the sporophyll. More than four is uncommon or rare — except in "forked" 

 or "branched" stamens — and represents morphologically complex androe- 

 cial structure. The larger number is nearly always eight, and this, at 

 least in some taxa, represents connation of two anthers. The morphology 

 of stamens with eight or more sporangia in families with greatly reduced 

 flowers, such as the Balanophoraceae, is uncertain. The apparently multi- 

 sporangiate condition in anthers, as in the Loranthaceae, Rhizophora- 

 ceae, Gentianaceae, represents partition of the sporogenous tissue by 

 sterile plates. Less than four sporangia in the anther is frequent and 

 represents a reduction from the basic four. The lost sporangia are nearly 

 always two; usually both are from one lateral half; rarely, the back 

 members of each half. A sporangium number of two is characteristic of 

 taxa of various rank: of many genera and of families — Epacridaceae, 

 Onagraceae, Labiatae, Lemnaceae; of tribes in some families where 

 other tribes have the normal four— Restionaceae, Stylidiaceae. Where 

 these two sporangia unite at maturity, the anther is termed imiJocuJar. 

 (Rarely, four sporangia unite to form a unilocular anther — Arisacnm, 

 Callitriche, some species of Chisia.) Reduction to a single sporangium, 

 with some trace of a second, has been i-eported in the small parasite, 

 Arceuthobium pusillum, where the reniform sporangium encircles an 

 erect connective ("columella"). Among the stamens of a flower, sporan- 

 gium number is variously reduced under zygornorphy; for example, in 

 some of the Proteaceae, one anther may have four sporangia, two others 

 have two each, and the fourth be sterile. The loss of sporangia is often 



