. An introduction to vegetable physiology. Plant physiology. THE DIFFERENTIATION OF THE PLANT-BODY 39 through the whole of the intercellular space system. As nearly every protoplast abuts in part upon a channel of this system, its necessary aeration is secured. Each proto- plast is thus in a somewhat intricate manner in contact with the external air,though really situated perhaps deep in the tissues of a plant of large dimensions. Like the aquatic plant, the terrestrial one thus pos- sesses a reservoir contain- ing an atmosphere which, ^^^ sb.^e^^k or a l^ticbi,. though its composition may l,
. An introduction to vegetable physiology. Plant physiology. THE DIFFERENTIATION OF THE PLANT-BODY 39 through the whole of the intercellular space system. As nearly every protoplast abuts in part upon a channel of this system, its necessary aeration is secured. Each proto- plast is thus in a somewhat intricate manner in contact with the external air,though really situated perhaps deep in the tissues of a plant of large dimensions. Like the aquatic plant, the terrestrial one thus pos- sesses a reservoir contain- ing an atmosphere which, ^^^ sb.^e^^k or a l^ticbi,. though its composition may l, lenticel; per, cork layer. not be exactly that of the exterior, yet contains oxygen for the need of the protoplasts and serves as the medium by which all surplus carbon dioxide is removed from them. This intercellular space system not only subserves the purpose of the gaseous interchanges of respiration, but ministers in two ways to the metabolic phenomena carried out by the plant. It permits the access of the atmospheric carbon dioxide to structures in the leaves which make it available for the construction of food material. It further is of great importance in helping to regulate the supply of water to the cells. We have seen that a transport system is differentiated which carries the water to them. This transport system does not, however, remove it from them subsequently. The protoplast can only get rid of water by the process of evaporation, and as it constantly needs a new supply, it must continuously exhale watery vapour to make room for the incoming stream. Such evaporation takes place into the intercellular spaces through the delicate cell- walls which abut upon them. The intercellular reservoir contains, therefore, an atmosphere which is charged almost,, if not quite, to saturation by aqueous vapour, and under ordinary atmospheric conditions this is being continually exhaled as long as an excess of water is passing through. Please note that these images are extracted f
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