The presence of a periodic acid-Schiff's (PAS) substance at the micropylar portion of the ovules of Paspalum orbiculare and three other species of Paspalum has been revealed by improved cytological techniques. The substance is located in the distal portion of the outer integument, especially at its edges, and in the micropyle, which is formed by the inner integument. A study of the origin of this substance in P. orbiculare indicates that it is produced from the cellular material of the dissolved cells in situ. The PAS substance is highly water soluble and may contain some protein. The final directional growth of the pollen tube into the filiform apparatus of the degenerated synergid is related to this substance. The role of the synergids in its formation is discussed.
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Chuan‐ying Chao (1971) studied this question.