. The essentials of botany. Botany. 228 BOTANY. young pollen-sacs undergo division into four parts, which become rounded and covered with a double coat or wall. The outer coat is often much thickened, and may be rough- ened by ridges or prickles (Fig. 128). 483. The pollen-cells germinate in moisture, by sending out a tube which is a prolongation of the inner coat. In some cases there are cells or nuclei in the cell or tube^ evi- dently representing the first stage (prothallium) in its last stages of suppression. The protoplasm of the cell passes freely down the tube to its extremity. 484. The
. The essentials of botany. Botany. 228 BOTANY. young pollen-sacs undergo division into four parts, which become rounded and covered with a double coat or wall. The outer coat is often much thickened, and may be rough- ened by ridges or prickles (Fig. 128). 483. The pollen-cells germinate in moisture, by sending out a tube which is a prolongation of the inner coat. In some cases there are cells or nuclei in the cell or tube^ evi- dently representing the first stage (prothallium) in its last stages of suppression. The protoplasm of the cell passes freely down the tube to its extremity. 484. The ovule-bearing leaves of Angiosperms bear still less resemblance to ordinary leaves than do the stamens. In the simpler cases the young leaf becomes curved so that its edges touch and finally grow together, forming the ovary, which usually tapers above into a style or stalk sup- porting a glandular structure, the stigma (Fig. 127, n). The whole ovule-bearing organ, com- posed of ovary, style, and stigma, is usually known as the pistil. In many plants several pistils grow together, and thus form a coro- ^ ,„ „ , pound pistil. Fio. 189.—very young ovules. * »c, OTUle-body; sc inner, and pr, 485. The OVuleS gTOW UpOn the outer, coats just beginning to or MO MmS °™'*'^'*'^' ''^^^^^ inner (, upper) surface of the leaf which forms the ovary, or at its base (Fig. 127), or more frequently upon its margins. At first it is a simple rounded outgrowth of a few cells; as it grows older a circular ridge arises upon it, which often is soon followed by another (Fig. 129, A and B). These ridges grow out and upwards so rapidly that they overtake and enclose the ovule-body, leaving but a small opening or 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 Bessey, Charles E. (Charles Edwin), 1845-1915. New York
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Keywords: ., bookcentury1800, bookdecade1890, bookpublisher, booksubjectbotany
