THE ULTRASTRUCTURE AND HISTOCHEMISTRY OF THE SYNERGIDS OF COTTON

The composition and ultrastructure of the synergids of cotton were studied. The cells were found to be surrounded by a partial wall composed of cellulose, hemicellulose, and pectins. The structure of the wall was observed to consist of an unusual fibrillar arrangement. The filiform apparatus was demonstrated to be an extension of the wall at the micropylar end of the cell. Large amounts of ER surround the filiform apparatus. Also associated with the latter are large numbers of plastids and mitochondria. The nucleus is large and contains a single, large nucleolus and, frequently, 1 or more micronucleoli. The nuclear membrane contains membrane‐bound vesicles but has few extensions into the cytoplasm. The ER is oriented parallel to the long axis of the cell and decreases in concentration from the micropylar to the chalazal end of the cell. Dictyosomes are common throughout the cell but are more numerous in the midportion where they are closely associated with the ER. The chalazal end of the cell is occupied by vacuoles rich in an inorganic compound which leaves a considerable residue of ash. Spherosome‐like bodies are common throughout the cell. Both the plastids and mitochondria show evidence of division. Ribosomes are numerous and are both free and associated with the ER, nucleus, plastids, and mitochondria. The function of the synergids is proposed to be the absorption, storage, and transport of compounds from the nucellus. On the basis of this function, it is suggested that the synergids act by providing material to the egg and the developing embryo and endosperm and that they are involved in the growth of the pollen tube into the embryo sac.