. Elementary botany. Botany. In comparing the female prothallium of the gymnosperms with that of the fern group we see a remarkable change has taken place. The female pro- thallium of the gymno- Ex ?2 r> sperms is very much A S ! reduced in size. Espe- cially, it no longer leads an independent existence from the sporophyte, as is the case with nearly all the fern group. It remains enclosed within the macrosporangium (in cycas if not fertilized it sometimes grows outside of the macrosporangium and becomes green), and derives its nourishment through it from the sporo- phyte, to which the latt
. Elementary botany. Botany. In comparing the female prothallium of the gymnosperms with that of the fern group we see a remarkable change has taken place. The female pro- thallium of the gymno- Ex ?2 r> sperms is very much A S ! reduced in size. Espe- cially, it no longer leads an independent existence from the sporophyte, as is the case with nearly all the fern group. It remains enclosed within the macrosporangium (in cycas if not fertilized it sometimes grows outside of the macrosporangium and becomes green), and derives its nourishment through it from the sporo- phyte, to which the latter remains organically con- nected. This condition of the female prothallium of the gymnosperms necessitated a special Gingko biloba. A, mature pollen grain ;/?, germinating adaptation of the male pollen grain, the branched tube entering among the cells ^vofh-llinm ;n order tint of the nucellus; Ex, exine (outer wall of spore); /\, pro- piomainum in oraei mac thallial cell; /\2, antheridial cell (divides later to form stalk the sperm cells may reach cell and generative cell); P%t vegetative cell; Va, vacuoles ; . Nct nucellus. (After drawings by Hirase and Ikeno.) and fertilize the egg Fig. 287. Gingko biloba, diagrammatic representation of the relation of pollen tube to the arche- gonium in the end of the nucellus. pt} pollen tube; 0, archegonium. (Alter drawing by and Ikeno.) 437. Gymnosperms are naked seed plants. — The pine, as we have seen, naked seeds. That is, the seeds are not enclosed within the carpel, but. 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 Atkinson, George Francis, 1854-1918. New York, H. Holt and company
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