. College botany; structure, physiology and economics of plants. Botany. 307 genera and 350 .specie^ and they ait found mostly in the tem- perate zones. The pine is a good type for study. A- a matter of convenience we will reverse our order of pres- entation and give the Sporophyte the first consideration. Tliese trees have roots and stems ver^' similar in structure to the Angio- sperm plants which we have already studied. However, the leaves are very much modified, ranging from flat blade-like struc- tures to narrow needles. The mesophyll is greatly reduced and the epidermis v
. College botany; structure, physiology and economics of plants. Botany. 307 genera and 350 .specie^ and they ait found mostly in the tem- perate zones. The pine is a good type for study. A- a matter of convenience we will reverse our order of pres- entation and give the Sporophyte the first consideration. Tliese trees have roots and stems ver^' similar in structure to the Angio- sperm plants which we have already studied. However, the leaves are very much modified, ranging from flat blade-like struc- tures to narrow needles. The mesophyll is greatly reduced and the epidermis ver\- pronounced compared with that of most Angiosperms. There are two t^•pes of cones, the pistillate or. Fig. 153,—(a) Pollen grain; (6) same ehoH-ing6xst division; (c) poUentube; (d) sporangium ehowingintegument, micropyleand archegonia: ^^J ^ameshowingensbryos; if) matureseed. ovulate and the stamiiude, which are composed of scales or sporo- phylls (modified leaves i arranged in spirals. TThen the pistillate cones are mature the macrosporophylls spread apart, exposing two ovules or macrosporangia en the upper surface of each. At the lower point of eaxjh macrosporangium are two processes or extensions of the integument; the opening between them is the micropyle. The inner part of the macrosporangium is called the nucellus and contains one or more maerospores which become the female prothaUia or Gametophytes. The archegonia are formed in the nucellus near the micropyle (Figs. , 153). The staminate cones are made up of mierosporophvlls which spread apart exposing two small sacs or anthers (microspo-. 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 Cook, Melville Thurston, 1869-1952. Philadelphia and London, J. B. Lippincott Company
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectbotany, bookyear1920
