File:Nature and development of plants (1907) (14589613030).jpg

Identifier: naturedevelopmen1907curt (find matches)
Title: Nature and development of plants
Year: 1907 (1900s)
Authors: Curtis, Carlton, C. (Carlton Clarence), b. 1864
Subjects: Plants Plants
Publisher: New York, H. Holt and company
Contributing Library: The LuEsther T Mertz Library, the New York Botanical Garden
Digitizing Sponsor: The LuEsther T Mertz Library, the New York Botanical Garden

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the resulting gameto-spore becomes surrounded by a thick wall and in this resting con-dition it tides the plant over seasons, such as the winter or drought,unfavorable for the growth of the plant. When conditions re-turn that permit the growth of the plant, the gametospore germi-nates by rupturing the outer wall and protruding the inner wallof the spore as a delicate tube (Fig. 107, B). As this tube con-tinues to elongate the characteristic plastids and cell partitionsarise, thus forming a new plant. The loss of motility in thereproductive process in this order may possibly be associatedwith their exposure to terrestrial conditions. They are oftenexposed to the soil, owing to the drying up of the water and ithas been suggested that they have consequently lost their mo-tility. Their mucilaginous coatings would be of great servicein enabling them to meet such conditions by retaining moisture,and indeed, they are often able to flourish in many damp placeswithout the aid of surface water.
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Fig. 108. Common forms of Desmids: ./, Closterium. B, Microsterias.C, Xanthidium. D, Straustrastrum. At left top view, at right side view.E, Desmidium forming a chain of plants. At righl end view of chain. DEVELOPMENT OF PLANTS 169 The Desmids.—A second group of the Zygnematales arestrictly unicellular plants known as Desmids (Fig. 108). Theyare the most attractive of unicellular plants and are of commonoccurrence associated with coarse algae. The desmids are elabo-rately and variously fashioned but can readily be recognized bythe fact that they consist of two similar halves (Fig. 109, A).The structure of the cells and the sexual method of reproductionis essentially the same as in the filamentous forms which haveprobably been derived from these unicellular plants. The asex-ual method of reproduction, however, is rather peculiar. Theregion connecting the two halves (Fig. 109, A, i), called the isth-mus, becomes somewhat elongated and swollen. Soon a con-striction appears midway betwe

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