1. A study is made of the development of the vascular supply for the floral parts of four genera of the Guttiferae-Moronoboideae,
Moronobea, Montrouziera,
Symphonia, and
Thysanostemon. Special reference is made to the androecium; all of these genera have characteristic fasciculate androecia.
2. It was found that in all plants examined siphonosteles are formed at the level from which the petal-stamen fascicle trace or stamen fascicle trace diverges. These steles arise directly from the receptacular stele, either independently or fused with the vascular supply to the petals. The five dissected siphonosteles formed branch off to form a vascular supply for each stamen after separation of the petal supply. The arrangement of the vascular supply for each stamen differs from genus to genus. In
Montrouziera and
Thysanostemon U-shaped bundles are formed, with the xylem entirely centrifugal. However, in
Moronobea the bundles formed at the same level are distributed quite irregularly. In the genus
Symphonia, two rows of irregularly placed bundles supplying each stamen were seen.
3. The siphonosteles seen at the level where fascicle traces formed, and the amphicribral bundles seen in the stamen supply of
Moronobea are among the most unusual types of vascular system found in angiosperm androecia.
4. There is a close phylogenetic affinity in the anatomical structure of the four genera studied. Fusion of the fascicles and reduction of the number of stamens per fascicle occurs. The genus
Symphonia apparently represents the ultimate stage of this specialization.
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