. Botany, with agricultural applications. Botany. 448 SPERMATOPHYTES (SEED PLANTS) when they are short and fleshy, they fit together Uke the kernels on an ear of Corn. The ovules are borne separately near the base of the megasporophyll and as shown in Figure 398. In some Cycads each megasporophyll bears only two ovules, while in others, as Figure 398 shows, a larger number may be present. In some Cycads the megasporophylls are much branched like foliage leaves, and the sporangia appear to be transformed lower branches or pinnae. Megasporophylls of this type suggest the relation- ship of sporop
. Botany, with agricultural applications. Botany. 448 SPERMATOPHYTES (SEED PLANTS) when they are short and fleshy, they fit together Uke the kernels on an ear of Corn. The ovules are borne separately near the base of the megasporophyll and as shown in Figure 398. In some Cycads each megasporophyll bears only two ovules, while in others, as Figure 398 shows, a larger number may be present. In some Cycads the megasporophylls are much branched like foliage leaves, and the sporangia appear to be transformed lower branches or pinnae. Megasporophylls of this type suggest the relation- ship of sporophylls to foliage leaves. The young megasporangium or ovule contains four megaspores, which are enclosed by two distinct coverings of sterile tissue. The inner covering is the nucellus, which surrounds and encloses. Fig. 398. — Ovulate strobilus and megasporophylls in Cycads. At the left, an ovulate strobilus; at the right, two types of megasporophylls, show- ing the ovules (o). the megaspores, and the outer one is the integument, which grows up from the base of the ovule and forms a covering over the nucellus. The integument is a protection for the nucellus, and, when the ovule develops into a seed, it is transformed into a seed coat. At the outer end of the megasporangium where the integu- ment closes over the nucellus, a small opening or micropyle is left which leads into a cavity, called the pollen chamber, into which a beak-Hke portion of the nucellus projects (Fig. 399). Female Gametophyte. — Only one of the four megaspores in the megasporangium develops. The other three disappear and all of the space and food is therefore given over to the develop- ment of one gametophyte. The megaspore germinates in the. 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 Martin, John N. (John Nathan), b. 1875. New Yo
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectbotany, bookyear1920
