. Plant life and plant uses; an elementary textbook, a foundation for the study of agriculture, domestic science or college botany. Botany. 442 THE VASCULAR PLANTS. from the strobili of lower plants only in that the megasporangia grow within a closed organ, — the ovary. Thus in flowers we find megasporangia hidden. This is new. Heretofore we have found them borne upon the surface of the megasporophylls. It was not necessary to cut open any inclosing structure in order to find them. But now, among all angio- sperms, we find that the carpels (megasporophylls) do not bear the ovules (megasporangi
. Plant life and plant uses; an elementary textbook, a foundation for the study of agriculture, domestic science or college botany. Botany. 442 THE VASCULAR PLANTS. from the strobili of lower plants only in that the megasporangia grow within a closed organ, — the ovary. Thus in flowers we find megasporangia hidden. This is new. Heretofore we have found them borne upon the surface of the megasporophylls. It was not necessary to cut open any inclosing structure in order to find them. But now, among all angio- sperms, we find that the carpels (megasporophylls) do not bear the ovules (megasporangia) upon their surface; they inclose them completely in a structure called the ovary. (See Figure 228.) A new task has been given to the pollen tube. Its journey has been extended. It must now penetrate more than the tissue of the ovule in order to reach the egg; it must penetrate also the tissues of the carpels which inclose the ovules. The carpels are usually united at the base into a compound ovary and extend upwards in the form of style and stigma, and all these tissues must be penetrated. The pollen tubes grow down from the stigma, through the style, and penetrate into the ovules at last. (See page 269.) Fig. 228. — Cross section of a young ovary of lily. There are two vertical rows of ovules in each of the three carpels which compose this ovary. The diagram indicates a single mega- spore within each of the ovules shown. The nucleus of this megaspore divides and redivides until an eight-celled female gametophyte results, such as is shown in Figure 230. Fig. 2 2g. — An ovary of lily shortly after fertilization has oc- curred. Figure 228 represents a. cross section of such an ovary when Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Coulter, John G. (John Gaylord), b. 1876. New York, Ameri
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