. Botany of the living plant. Botany. CONIFERAE: THE SCOTS PINE 311 these originates from a single superficial cell of the prothallus, and consists of a large nucleated ovum, with a small lenticular venLral- canal-cell lying above it, which is cut off from the ovum shortly before fertilisation. Covering this is a group of cells two or more tiers in depth, forming the channel of the neck (Fig. 254, A). The ovum of Pinus, as is not uncommonly the case in Gymnosperms, is large Fic. 253. Median longitudinal section of an ovule of Picca cxccUa at time of fertilisation, i? = embryo-sac filled w
. Botany of the living plant. Botany. CONIFERAE: THE SCOTS PINE 311 these originates from a single superficial cell of the prothallus, and consists of a large nucleated ovum, with a small lenticular venLral- canal-cell lying above it, which is cut off from the ovum shortly before fertilisation. Covering this is a group of cells two or more tiers in depth, forming the channel of the neck (Fig. 254, A). The ovum of Pinus, as is not uncommonly the case in Gymnosperms, is large Fic. 253. Median longitudinal section of an ovule of Picca cxccUa at time of fertilisation, i? = embryo-sac filled with tissue of the female protliallus. a = archegoniunt, showing venter (a) and necl; (f). â ;j = nucleus of ovum. j!c = nncellus. ^ = pollen- grains. f âpollen-tube, i âintegument. ( n 9.} (.-^fter Strasburger.) enough to be seen with the naked eye. The archegonia lie in a slight depression of the surface of the prothallus. The last step before fertilisation is the collapse of the ventral-canal-cell, which takes no direct part in propagation. In the Scots Pine a whole year elapses between the pollination of the young pink cone and the act of fertilisation. But in Conifers generally the times are different. With or without a lengthened interval each pollen-grain, germinating on the apex of the iiucellus, forms a pollen-tube, which penetrates the nucellus, passing towards. 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 Bower, F. O. (Frederick Orpen), 1855-1948. London, Macmillan and co. , limited
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1919
