Development of the Macrogametophyte and Embryo of Daucus carota

This paper is concerned with the development of the female gametophyte, the pollen tubes, and the embryo of Daucus carota. 2. A single archesporial cell functions directly as a macrospore mother cell which produces a linear tetrad of macrospores. 3. The macrogametophyte, which arises from the chalazal macrospore, is of the 7-celled type characteristic of most angiosperms. 4. The presence of a cellulose filiform apparatus was demonstrated by microchemical tests. 5. The structure and path of the pollen tubes were investigated. Tubes were found to grow intercellularly down through the conducting tissue of the style to its base, and then superficially along a groove leading to a canal communicating with each locule. Tubes growing down one style may enter the locule immediately below or grow through the transverse canal and into the other locule. 6. A filamentous 8-celled embryo is usually formed before longitudinal divisions occur. The three cells farthest from the micropyle give rise to all of the embryo except the root tip. The other five cells give rise to the root tip and the suspensor. 7. Development of the embryo was considered in the light of Souèges' theory that the 4-celled embryo is the critical stage in development, and that for any given species the four cells always give rise to the same parts of the embryo. In Daucus the mature embryo may arise entirely from the distal cell of the 4-celled embryo, or from the distal cell and derivatives of the cell next to it. Soueges' further generalization that embryonal development is usually characteristic throughout a family does not appear to hold in the Umbelliferae, as is shown by a comparison of Daucus with his account of the embryogeny of Carum.